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 $182.92   10.358%   $201.8669   $201.87   $201.85   $201.90  
  Purchase #2 $153.97   8.319%   $166.7788   $166.78   $166.80   $166.80  
  Purchase #3 $70.27   4.624%   $73.5193   $73.52   $73.50   $73.50  
  Purchase #4 $127.64   6.770%   $136.2812   $136.28   $136.30   $136.30  
  Purchase #5 $133.72   4.220%   $139.363   $139.36   $139.35   $139.40  
  Purchase #6 $119.83   12.153%   $134.3929   $134.39   $134.40   $134.40  
  Purchase #7 $120.50   12.343%   $135.3733   $135.37   $135.35   $135.40  
  7 purchase totals = $908.85       $987.5754   $987.57   $987.55   $987.70