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 $145.76   7.106%   $156.1177   $156.12   $156.10   $156.10  
  Purchase #2 $67.77   12.662%   $76.351   $76.35   $76.35   $76.40  
  Purchase #3 $24.96   9.382%   $27.3017   $27.30   $27.30   $27.30  
  Purchase #4 $162.48   8.589%   $176.4354   $176.44   $176.45   $176.40  
  Purchase #5 $207.66   13.443%   $235.5757   $235.58   $235.60   $235.60  
  Purchase #6 $179.72   8.498%   $194.9926   $194.99   $195.00   $195.00  
  Purchase #7 $143.78   9.733%   $157.7741   $157.77   $157.75   $157.80  
  7 purchase totals = $932.13       $1,024.5482   $1,024.55   $1,024.55   $1,024.60