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 $246.89   8.753%   $268.5003   $268.50   $268.50   $268.50  
  Purchase #2 $54.43   8.278%   $58.9357   $58.94   $58.95   $58.90  
  Purchase #3 $75.61   6.695%   $80.6721   $80.67   $80.65   $80.70  
  Purchase #4 $207.94   4.415%   $217.1206   $217.12   $217.10   $217.10  
  Purchase #5 $13.53   7.874%   $14.5954   $14.60   $14.60   $14.60  
  Purchase #6 $13.80   11.763%   $15.4233   $15.42   $15.40   $15.40  
  Purchase #7 $165.34   6.475%   $176.0458   $176.05   $176.05   $176.00  
  7 purchase totals = $777.54       $831.2932   $831.30   $831.25   $831.20