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 $210.76   6.773%   $225.0348   $225.03   $225.05   $225.00  
  Purchase #2 $202.62   7.131%   $217.0688   $217.07   $217.05   $217.10  
  Purchase #3 $68.33   12.279%   $76.7202   $76.72   $76.70   $76.70  
  Purchase #4 $125.61   6.209%   $133.4091   $133.41   $133.40   $133.40  
  Purchase #5 $105.38   13.359%   $119.4577   $119.46   $119.45   $119.50  
  Purchase #6 $33.26   11.287%   $37.0141   $37.01   $37.00   $37.00  
  Purchase #7 $204.73   12.245%   $229.7992   $229.80   $229.80   $229.80  
  7 purchase totals = $950.69       $1,038.5039   $1,038.50   $1,038.45   $1,038.50