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 $81.26   7.555%   $87.3992   $87.40   $87.40   $87.40  
  Purchase #2 $215.95   9.524%   $236.5171   $236.52   $236.50   $236.50  
  Purchase #3 $176.42   5.597%   $186.2942   $186.29   $186.30   $186.30  
  Purchase #4 $65.88   11.250%   $73.2915   $73.29   $73.30   $73.30  
  Purchase #5 $239.97   12.517%   $270.007   $270.01   $270.00   $270.00  
  Purchase #6 $209.68   10.863%   $232.4575   $232.46   $232.45   $232.50  
  Purchase #7 $243.91   9.584%   $267.2863   $267.29   $267.30   $267.30  
  7 purchase totals = $1,233.07       $1,353.2528   $1,353.26   $1,353.25   $1,353.30