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 $69.32   8.564%   $75.2566   $75.26   $75.25   $75.30  
  Purchase #2 $174.57   10.673%   $193.2019   $193.20   $193.20   $193.20  
  Purchase #3 $47.35   10.655%   $52.3951   $52.40   $52.40   $52.40  
  Purchase #4 $100.82   9.829%   $110.7296   $110.73   $110.75   $110.70  
  Purchase #5 $233.61   7.627%   $251.4274   $251.43   $251.45   $251.40  
  Purchase #6 $127.90   12.250%   $143.5678   $143.57   $143.55   $143.60  
  Purchase #7 $105.43   10.684%   $116.6941   $116.69   $116.70   $116.70  
  7 purchase totals = $859.00       $943.2725   $943.28   $943.30   $943.30