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 $48.52   9.632%   $53.1934   $53.19   $53.20   $53.20  
  Purchase #2 $215.42   12.669%   $242.7116   $242.71   $242.70   $242.70  
  Purchase #3 $190.97   9.839%   $209.7595   $209.76   $209.75   $209.80  
  Purchase #4 $55.64   7.244%   $59.6706   $59.67   $59.65   $59.70  
  Purchase #5 $34.79   10.457%   $38.428   $38.43   $38.45   $38.40  
  Purchase #6 $163.73   10.149%   $180.347   $180.35   $180.35   $180.30  
  Purchase #7 $205.76   3.211%   $212.367   $212.37   $212.35   $212.40  
  7 purchase totals = $914.83       $996.4771   $996.48   $996.45   $996.50