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 $96.83   5.256%   $101.9194   $101.92   $101.90   $101.90  
  Purchase #2 $231.86   11.349%   $258.1738   $258.17   $258.15   $258.20  
  Purchase #3 $45.91   4.845%   $48.1343   $48.13   $48.15   $48.10  
  Purchase #4 $125.31   7.703%   $134.9626   $134.96   $134.95   $135.00  
  Purchase #5 $53.97   8.430%   $58.5197   $58.52   $58.50   $58.50  
  Purchase #6 $213.67   5.229%   $224.8428   $224.84   $224.85   $224.80  
  Purchase #7 $187.54   11.397%   $208.9139   $208.91   $208.90   $208.90  
  7 purchase totals = $955.09       $1,035.4665   $1,035.45   $1,035.40   $1,035.40