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 $244.54   8.487%   $265.2941   $265.29   $265.30   $265.30  
  Purchase #2 $25.67   5.527%   $27.0888   $27.09   $27.10   $27.10  
  Purchase #3 $131.39   6.752%   $140.2615   $140.26   $140.25   $140.30  
  Purchase #4 $185.40   9.553%   $203.1113   $203.11   $203.10   $203.10  
  Purchase #5 $94.70   8.269%   $102.5307   $102.53   $102.55   $102.50  
  Purchase #6 $36.27   8.194%   $39.242   $39.24   $39.25   $39.20  
  Purchase #7 $170.51   3.115%   $175.8214   $175.82   $175.80   $175.80  
  7 purchase totals = $888.48       $953.3498   $953.34   $953.35   $953.30