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 $60.93   7.467%   $65.4796   $65.48   $65.50   $65.50  
  Purchase #2 $118.91   8.843%   $129.4252   $129.43   $129.45   $129.40  
  Purchase #3 $244.61   13.163%   $276.808   $276.81   $276.80   $276.80  
  Purchase #4 $153.46   8.860%   $167.0566   $167.06   $167.05   $167.10  
  Purchase #5 $223.81   11.517%   $249.5862   $249.59   $249.60   $249.60  
  Purchase #6 $63.67   13.551%   $72.2979   $72.30   $72.30   $72.30  
  Purchase #7 $203.63   7.754%   $219.4195   $219.42   $219.40   $219.40  
  7 purchase totals = $1,069.02       $1,180.0730   $1,180.09   $1,180.10   $1,180.10