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 $7.26   4.300%   $7.5722   $7.57   $7.55   $7.60  
  Purchase #2 $129.73   6.484%   $138.1417   $138.14   $138.15   $138.10  
  Purchase #3 $5.56   13.644%   $6.3186   $6.32   $6.30   $6.30  
  Purchase #4 $43.75   3.277%   $45.1837   $45.18   $45.20   $45.20  
  Purchase #5 $28.81   13.666%   $32.7472   $32.75   $32.75   $32.70  
  Purchase #6 $26.55   4.478%   $27.7389   $27.74   $27.75   $27.70  
  Purchase #7 $144.58   10.208%   $159.3387   $159.34   $159.35   $159.30  
  7 purchase totals = $386.24       $417.0410   $417.04   $417.05   $416.90