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 $68.36   8.649%   $74.2725   $74.27   $74.25   $74.30  
  Purchase #2 $76.59   7.452%   $82.2975   $82.30   $82.30   $82.30  
  Purchase #3 $236.30   13.754%   $268.8007   $268.80   $268.80   $268.80  
  Purchase #4 $160.68   11.584%   $179.2932   $179.29   $179.30   $179.30  
  Purchase #5 $203.34   11.846%   $227.4277   $227.43   $227.45   $227.40  
  Purchase #6 $12.25   5.455%   $12.9182   $12.92   $12.90   $12.90  
  Purchase #7 $83.60   13.620%   $94.9863   $94.99   $95.00   $95.00  
  7 purchase totals = $841.12       $939.9961   $940.00   $940.00   $940.00