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 $59.89   10.760%   $66.3342   $66.33   $66.35   $66.30  
  Purchase #2 $88.88   5.333%   $93.62   $93.62   $93.60   $93.60  
  Purchase #3 $169.45   4.142%   $176.4686   $176.47   $176.45   $176.50  
  Purchase #4 $48.87   3.546%   $50.6029   $50.60   $50.60   $50.60  
  Purchase #5 $100.38   6.204%   $106.6076   $106.61   $106.60   $106.60  
  Purchase #6 $134.37   13.182%   $152.0827   $152.08   $152.10   $152.10  
  Purchase #7 $160.79   6.130%   $170.6464   $170.65   $170.65   $170.60  
  7 purchase totals = $762.63       $816.3624   $816.36   $816.35   $816.30