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 $237.96   9.244%   $259.957   $259.96   $259.95   $260.00  
  Purchase #2 $17.87   4.479%   $18.6704   $18.67   $18.65   $18.70  
  Purchase #3 $89.39   13.561%   $101.5122   $101.51   $101.50   $101.50  
  Purchase #4 $211.68   3.340%   $218.7501   $218.75   $218.75   $218.80  
  Purchase #5 $235.64   13.336%   $267.065   $267.07   $267.05   $267.10  
  Purchase #6 $87.27   3.568%   $90.3838   $90.38   $90.40   $90.40  
  Purchase #7 $79.62   11.736%   $88.9642   $88.96   $88.95   $89.00  
  7 purchase totals = $959.43       $1,045.3027   $1,045.30   $1,045.25   $1,045.50