Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $187.55   5.757%   $198.3473   $198.35   $198.35   $198.30  
  Purchase #2 $243.63   13.553%   $276.6492   $276.65   $276.65   $276.60  
  Purchase #3 $101.89   11.521%   $113.6287   $113.63   $113.65   $113.60  
  Purchase #4 $176.90   10.466%   $195.4144   $195.41   $195.40   $195.40  
  Purchase #5 $200.38   5.110%   $210.6194   $210.62   $210.60   $210.60  
  Purchase #6 $113.35   3.631%   $117.4657   $117.47   $117.45   $117.50  
  Purchase #7 $155.64   7.595%   $167.4609   $167.46   $167.45   $167.50  
  7 purchase totals = $1,179.34       $1,279.5856   $1,279.59   $1,279.55   $1,279.50