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 $202.53   10.650%   $224.0994   $224.10   $224.10   $224.10  
  Purchase #2 $57.74   6.766%   $61.6467   $61.65   $61.65   $61.60  
  Purchase #3 $83.53   7.540%   $89.8282   $89.83   $89.85   $89.80  
  Purchase #4 $162.53   9.288%   $177.6258   $177.63   $177.65   $177.60  
  Purchase #5 $93.70   11.412%   $104.393   $104.39   $104.40   $104.40  
  Purchase #6 $185.38   10.312%   $204.4964   $204.50   $204.50   $204.50  
  Purchase #7 $88.49   6.437%   $94.1861   $94.19   $94.20   $94.20  
  7 purchase totals = $873.90       $956.2756   $956.29   $956.35   $956.20