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 $116.33   9.739%   $127.6594   $127.66   $127.65   $127.70  
  Purchase #2 $33.27   7.304%   $35.7   $35.70   $35.70   $35.70  
  Purchase #3 $194.92   6.687%   $207.9543   $207.95   $207.95   $208.00  
  Purchase #4 $125.52   5.228%   $132.0822   $132.08   $132.10   $132.10  
  Purchase #5 $67.57   7.513%   $72.6465   $72.65   $72.65   $72.60  
  Purchase #6 $188.83   13.392%   $214.1181   $214.12   $214.10   $214.10  
  Purchase #7 $68.60   11.214%   $76.2928   $76.29   $76.30   $76.30  
  7 purchase totals = $795.04       $866.4533   $866.45   $866.45   $866.50