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 $85.93   10.351%   $94.8246   $94.82   $94.80   $94.80  
  Purchase #2 $93.30   5.622%   $98.5453   $98.55   $98.55   $98.50  
  Purchase #3 $6.71   8.184%   $7.2591   $7.26   $7.25   $7.30  
  Purchase #4 $102.79   7.434%   $110.4314   $110.43   $110.45   $110.40  
  Purchase #5 $200.31   6.654%   $213.6386   $213.64   $213.65   $213.60  
  Purchase #6 $146.48   8.441%   $158.8444   $158.84   $158.85   $158.80  
  Purchase #7 $248.75   3.693%   $257.9363   $257.94   $257.95   $257.90  
  7 purchase totals = $884.27       $941.4797   $941.48   $941.50   $941.30