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 $41.49   12.169%   $46.5389   $46.54   $46.55   $46.50  
  Purchase #2 $224.35   5.478%   $236.6399   $236.64   $236.65   $236.60  
  Purchase #3 $165.37   3.774%   $171.6111   $171.61   $171.60   $171.60  
  Purchase #4 $20.94   11.329%   $23.3123   $23.31   $23.30   $23.30  
  Purchase #5 $237.45   4.393%   $247.8812   $247.88   $247.90   $247.90  
  Purchase #6 $59.65   11.419%   $66.4614   $66.46   $66.45   $66.50  
  Purchase #7 $175.78   5.188%   $184.8995   $184.90   $184.90   $184.90  
  7 purchase totals = $925.03       $977.3443   $977.34   $977.35   $977.30