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 $45.70   4.390%   $47.7062   $47.71   $47.70   $47.70  
  Purchase #2 $59.53   13.102%   $67.3296   $67.33   $67.35   $67.30  
  Purchase #3 $84.41   3.406%   $87.285   $87.29   $87.30   $87.30  
  Purchase #4 $99.42   13.432%   $112.7741   $112.77   $112.75   $112.80  
  Purchase #5 $55.80   11.379%   $62.1495   $62.15   $62.15   $62.10  
  Purchase #6 $145.59   13.613%   $165.4092   $165.41   $165.40   $165.40  
  Purchase #7 $197.83   6.431%   $210.5524   $210.55   $210.55   $210.60  
  7 purchase totals = $688.28       $753.2060   $753.21   $753.20   $753.20