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 $59.35   9.870%   $65.2078   $65.21   $65.20   $65.20  
  Purchase #2 $125.68   4.702%   $131.5895   $131.59   $131.60   $131.60  
  Purchase #3 $151.45   5.211%   $159.3421   $159.34   $159.35   $159.30  
  Purchase #4 $173.85   8.610%   $188.8185   $188.82   $188.80   $188.80  
  Purchase #5 $197.94   13.309%   $224.2838   $224.28   $224.30   $224.30  
  Purchase #6 $83.48   11.106%   $92.7513   $92.75   $92.75   $92.80  
  Purchase #7 $164.72   7.737%   $177.4644   $177.46   $177.45   $177.50  
  7 purchase totals = $956.47       $1,039.4574   $1,039.45   $1,039.45   $1,039.50