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 $236.49   5.481%   $249.452   $249.45   $249.45   $249.50  
  Purchase #2 $110.87   5.229%   $116.6674   $116.67   $116.65   $116.70  
  Purchase #3 $197.64   13.687%   $224.691   $224.69   $224.70   $224.70  
  Purchase #4 $80.82   13.831%   $91.9982   $92.00   $92.00   $92.00  
  Purchase #5 $146.97   6.503%   $156.5275   $156.53   $156.55   $156.50  
  Purchase #6 $41.73   11.120%   $46.3704   $46.37   $46.35   $46.40  
  Purchase #7 $189.75   3.175%   $195.7746   $195.77   $195.75   $195.80  
  7 purchase totals = $1,004.27       $1,081.4811   $1,081.48   $1,081.45   $1,081.60