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 $215.62   13.370%   $244.4484   $244.45   $244.45   $244.40  
  Purchase #2 $227.48   12.248%   $255.3418   $255.34   $255.35   $255.30  
  Purchase #3 $106.62   8.651%   $115.8437   $115.84   $115.85   $115.80  
  Purchase #4 $68.83   11.242%   $76.5679   $76.57   $76.55   $76.60  
  Purchase #5 $241.66   7.350%   $259.422   $259.42   $259.40   $259.40  
  Purchase #6 $35.73   5.859%   $37.8234   $37.82   $37.80   $37.80  
  Purchase #7 $5.67   10.205%   $6.2486   $6.25   $6.25   $6.20  
  7 purchase totals = $901.61       $995.6958   $995.69   $995.65   $995.50