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 $66.91   9.777%   $73.4518   $73.45   $73.45   $73.50  
  Purchase #2 $221.49   9.605%   $242.7641   $242.76   $242.75   $242.80  
  Purchase #3 $169.96   12.693%   $191.533   $191.53   $191.55   $191.50  
  Purchase #4 $224.95   12.504%   $253.0777   $253.08   $253.10   $253.10  
  Purchase #5 $32.83   6.563%   $34.9846   $34.98   $35.00   $35.00  
  Purchase #6 $116.62   8.306%   $126.3065   $126.31   $126.30   $126.30  
  Purchase #7 $232.85   5.270%   $245.1212   $245.12   $245.10   $245.10  
  7 purchase totals = $1,065.61       $1,167.2389   $1,167.23   $1,167.25   $1,167.30