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 $177.57   10.114%   $195.5294   $195.53   $195.55   $195.50  
  Purchase #2 $51.52   3.430%   $53.2871   $53.29   $53.30   $53.30  
  Purchase #3 $104.53   12.184%   $117.2659   $117.27   $117.25   $117.30  
  Purchase #4 $160.62   6.224%   $170.617   $170.62   $170.60   $170.60  
  Purchase #5 $161.70   7.114%   $173.2033   $173.20   $173.20   $173.20  
  Purchase #6 $27.82   3.512%   $28.797   $28.80   $28.80   $28.80  
  Purchase #7 $203.90   8.582%   $221.3987   $221.40   $221.40   $221.40  
  7 purchase totals = $887.66       $960.0984   $960.11   $960.10   $960.10