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 $189.36   3.261%   $195.535   $195.54   $195.55   $195.50  
  Purchase #2 $44.70   8.113%   $48.3265   $48.33   $48.35   $48.30  
  Purchase #3 $44.71   4.222%   $46.5977   $46.60   $46.60   $46.60  
  Purchase #4 $220.61   6.598%   $235.1658   $235.17   $235.15   $235.20  
  Purchase #5 $169.34   6.668%   $180.6316   $180.63   $180.65   $180.60  
  Purchase #6 $148.49   5.766%   $157.0519   $157.05   $157.05   $157.10  
  Purchase #7 $68.29   11.266%   $75.9836   $75.98   $76.00   $76.00  
  7 purchase totals = $885.50       $939.2921   $939.30   $939.35   $939.30