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 $48.39   4.147%   $50.3967   $50.40   $50.40   $50.40  
  Purchase #2 $244.38   11.697%   $272.9651   $272.97   $272.95   $273.00  
  Purchase #3 $32.94   3.735%   $34.1703   $34.17   $34.15   $34.20  
  Purchase #4 $190.87   11.820%   $213.4308   $213.43   $213.45   $213.40  
  Purchase #5 $235.62   13.787%   $268.1049   $268.10   $268.10   $268.10  
  Purchase #6 $147.89   6.399%   $157.3535   $157.35   $157.35   $157.40  
  Purchase #7 $212.46   6.836%   $226.9838   $226.98   $227.00   $227.00  
  7 purchase totals = $1,112.55       $1,223.4051   $1,223.40   $1,223.40   $1,223.50