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 $115.94   3.265%   $119.7254   $119.73   $119.75   $119.70  
  Purchase #2 $169.71   7.606%   $182.6181   $182.62   $182.60   $182.60  
  Purchase #3 $85.27   12.851%   $96.228   $96.23   $96.25   $96.20  
  Purchase #4 $63.33   8.123%   $68.4743   $68.47   $68.45   $68.50  
  Purchase #5 $213.72   11.350%   $237.9772   $237.98   $238.00   $238.00  
  Purchase #6 $9.67   7.248%   $10.3709   $10.37   $10.35   $10.40  
  Purchase #7 $42.55   4.786%   $44.5864   $44.59   $44.60   $44.60  
  7 purchase totals = $700.19       $759.9803   $759.99   $760.00   $760.00