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 $60.98   4.415%   $63.6723   $63.67   $63.65   $63.70  
  Purchase #2 $168.28   12.754%   $189.7424   $189.74   $189.75   $189.70  
  Purchase #3 $228.27   5.448%   $240.7061   $240.71   $240.70   $240.70  
  Purchase #4 $103.50   13.834%   $117.8182   $117.82   $117.80   $117.80  
  Purchase #5 $132.65   13.853%   $151.026   $151.03   $151.05   $151.00  
  Purchase #6 $240.46   12.712%   $271.0273   $271.03   $271.05   $271.00  
  Purchase #7 $224.64   10.233%   $247.6274   $247.63   $247.65   $247.60  
  7 purchase totals = $1,158.78       $1,281.6197   $1,281.63   $1,281.65   $1,281.50