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 $227.40   12.448%   $255.7068   $255.71   $255.70   $255.70  
  Purchase #2 $43.98   7.871%   $47.4417   $47.44   $47.45   $47.40  
  Purchase #3 $178.61   10.803%   $197.9052   $197.91   $197.90   $197.90  
  Purchase #4 $79.57   11.672%   $88.8574   $88.86   $88.85   $88.90  
  Purchase #5 $216.78   7.102%   $232.1757   $232.18   $232.20   $232.20  
  Purchase #6 $132.49   4.624%   $138.6163   $138.62   $138.60   $138.60  
  Purchase #7 $100.43   10.380%   $110.8546   $110.85   $110.85   $110.90  
  7 purchase totals = $979.26       $1,071.5577   $1,071.57   $1,071.55   $1,071.60