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 $85.39   11.605%   $95.2995   $95.30   $95.30   $95.30  
  Purchase #2 $74.94   8.399%   $81.2342   $81.23   $81.25   $81.20  
  Purchase #3 $188.60   4.681%   $197.4284   $197.43   $197.45   $197.40  
  Purchase #4 $83.75   5.641%   $88.4743   $88.47   $88.45   $88.50  
  Purchase #5 $54.97   10.781%   $60.8963   $60.90   $60.90   $60.90  
  Purchase #6 $220.66   13.286%   $249.9769   $249.98   $250.00   $250.00  
  Purchase #7 $23.82   3.694%   $24.6999   $24.70   $24.70   $24.70  
  7 purchase totals = $732.13       $798.0095   $798.01   $798.05   $798.00