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 $50.53   5.537%   $53.3278   $53.33   $53.35   $53.30  
  Purchase #2 $216.89   8.671%   $235.6965   $235.70   $235.70   $235.70  
  Purchase #3 $184.72   8.571%   $200.5524   $200.55   $200.55   $200.60  
  Purchase #4 $121.99   10.840%   $135.2137   $135.21   $135.20   $135.20  
  Purchase #5 $119.53   5.796%   $126.458   $126.46   $126.45   $126.50  
  Purchase #6 $61.97   10.605%   $68.5419   $68.54   $68.55   $68.50  
  Purchase #7 $92.41   9.419%   $101.1141   $101.11   $101.10   $101.10  
  7 purchase totals = $848.04       $920.9044   $920.90   $920.90   $920.90