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 $52.76   6.602%   $56.2432   $56.24   $56.25   $56.20  
  Purchase #2 $208.93   10.393%   $230.6441   $230.64   $230.65   $230.60  
  Purchase #3 $120.36   3.460%   $124.5245   $124.52   $124.50   $124.50  
  Purchase #4 $84.78   8.425%   $91.9227   $91.92   $91.90   $91.90  
  Purchase #5 $229.42   13.501%   $260.394   $260.39   $260.40   $260.40  
  Purchase #6 $99.79   12.200%   $111.9644   $111.96   $111.95   $112.00  
  Purchase #7 $143.91   11.786%   $160.8712   $160.87   $160.85   $160.90  
  7 purchase totals = $939.95       $1,036.5641   $1,036.54   $1,036.50   $1,036.50