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 $238.61   10.650%   $264.022   $264.02   $264.00   $264.00  
  Purchase #2 $208.93   7.769%   $225.1618   $225.16   $225.15   $225.20  
  Purchase #3 $32.91   10.170%   $36.2569   $36.26   $36.25   $36.30  
  Purchase #4 $239.40   6.620%   $255.2483   $255.25   $255.25   $255.20  
  Purchase #5 $85.64   7.370%   $91.9517   $91.95   $91.95   $92.00  
  Purchase #6 $97.83   4.568%   $102.2989   $102.30   $102.30   $102.30  
  Purchase #7 $46.65   3.829%   $48.4362   $48.44   $48.45   $48.40  
  7 purchase totals = $949.97       $1,023.3758   $1,023.38   $1,023.35   $1,023.40