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 $180.46   3.317%   $186.4459   $186.45   $186.45   $186.40  
  Purchase #2 $210.33   9.667%   $230.6626   $230.66   $230.65   $230.70  
  Purchase #3 $231.60   10.682%   $256.3395   $256.34   $256.35   $256.30  
  Purchase #4 $34.72   7.218%   $37.2261   $37.23   $37.25   $37.20  
  Purchase #5 $159.83   3.517%   $165.4512   $165.45   $165.45   $165.50  
  Purchase #6 $226.50   4.421%   $236.5136   $236.51   $236.50   $236.50  
  Purchase #7 $126.95   6.291%   $134.9364   $134.94   $134.95   $134.90  
  7 purchase totals = $1,170.39       $1,247.5753   $1,247.58   $1,247.60   $1,247.50