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 $47.86   10.216%   $52.7494   $52.75   $52.75   $52.70  
  Purchase #2 $244.97   4.571%   $256.1676   $256.17   $256.15   $256.20  
  Purchase #3 $63.55   6.143%   $67.4539   $67.45   $67.45   $67.50  
  Purchase #4 $20.56   13.434%   $23.322   $23.32   $23.30   $23.30  
  Purchase #5 $157.37   13.676%   $178.8919   $178.89   $178.90   $178.90  
  Purchase #6 $238.58   8.561%   $259.0048   $259.00   $259.00   $259.00  
  Purchase #7 $168.73   12.532%   $189.8752   $189.88   $189.90   $189.90  
  7 purchase totals = $941.62       $1,027.4648   $1,027.46   $1,027.45   $1,027.50