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 $126.61   5.797%   $133.9496   $133.95   $133.95   $133.90  
  Purchase #2 $188.56   8.814%   $205.1797   $205.18   $205.20   $205.20  
  Purchase #3 $37.32   5.204%   $39.2621   $39.26   $39.25   $39.30  
  Purchase #4 $236.93   13.458%   $268.816   $268.82   $268.80   $268.80  
  Purchase #5 $113.61   10.169%   $125.163   $125.16   $125.15   $125.20  
  Purchase #6 $45.95   3.791%   $47.692   $47.69   $47.70   $47.70  
  Purchase #7 $13.44   6.302%   $14.287   $14.29   $14.30   $14.30  
  7 purchase totals = $762.42       $834.3494   $834.35   $834.35   $834.40