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 $60.67   8.671%   $65.9307   $65.93   $65.95   $65.90  
  Purchase #2 $149.73   6.309%   $159.1765   $159.18   $159.20   $159.20  
  Purchase #3 $83.44   4.779%   $87.4276   $87.43   $87.45   $87.40  
  Purchase #4 $157.90   5.487%   $166.564   $166.56   $166.55   $166.60  
  Purchase #5 $53.48   9.673%   $58.6531   $58.65   $58.65   $58.70  
  Purchase #6 $53.39   9.335%   $58.374   $58.37   $58.35   $58.40  
  Purchase #7 $156.44   10.749%   $173.2557   $173.26   $173.25   $173.30  
  7 purchase totals = $715.05       $769.3816   $769.38   $769.40   $769.50