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 $48.67   10.788%   $53.9205   $53.92   $53.90   $53.90  
  Purchase #2 $124.76   3.621%   $129.2776   $129.28   $129.30   $129.30  
  Purchase #3 $64.60   13.612%   $73.3934   $73.39   $73.40   $73.40  
  Purchase #4 $55.54   5.355%   $58.5142   $58.51   $58.50   $58.50  
  Purchase #5 $211.48   3.787%   $219.4887   $219.49   $219.50   $219.50  
  Purchase #6 $111.67   11.350%   $124.3445   $124.34   $124.35   $124.30  
  Purchase #7 $155.97   5.187%   $164.0602   $164.06   $164.05   $164.10  
  7 purchase totals = $772.69       $822.9991   $822.99   $823.00   $823.00