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 $42.67   10.205%   $47.0245   $47.02   $47.00   $47.00  
  Purchase #2 $142.87   4.682%   $149.5592   $149.56   $149.55   $149.60  
  Purchase #3 $48.29   13.158%   $54.644   $54.64   $54.65   $54.60  
  Purchase #4 $130.63   4.579%   $136.6115   $136.61   $136.60   $136.60  
  Purchase #5 $23.39   6.132%   $24.8243   $24.82   $24.80   $24.80  
  Purchase #6 $235.64   6.363%   $250.6338   $250.63   $250.65   $250.60  
  Purchase #7 $66.89   5.384%   $70.4914   $70.49   $70.50   $70.50  
  7 purchase totals = $690.38       $733.7887   $733.77   $733.75   $733.70