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 $235.32   4.862%   $246.7613   $246.76   $246.75   $246.80  
  Purchase #2 $116.62   8.599%   $126.6482   $126.65   $126.65   $126.60  
  Purchase #3 $153.90   9.508%   $168.5328   $168.53   $168.55   $168.50  
  Purchase #4 $202.74   10.537%   $224.1027   $224.10   $224.10   $224.10  
  Purchase #5 $7.46   8.648%   $8.1051   $8.11   $8.10   $8.10  
  Purchase #6 $31.97   11.238%   $35.5628   $35.56   $35.55   $35.60  
  Purchase #7 $56.82   7.485%   $61.073   $61.07   $61.05   $61.10  
  7 purchase totals = $804.83       $870.7859   $870.78   $870.75   $870.80