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 $86.72   12.479%   $97.5418   $97.54   $97.55   $97.50  
  Purchase #2 $103.36   13.808%   $117.6319   $117.63   $117.65   $117.60  
  Purchase #3 $153.28   13.742%   $174.3437   $174.34   $174.35   $174.30  
  Purchase #4 $50.38   3.749%   $52.2687   $52.27   $52.25   $52.30  
  Purchase #5 $234.48   9.608%   $257.0088   $257.01   $257.00   $257.00  
  Purchase #6 $122.57   6.282%   $130.2698   $130.27   $130.25   $130.30  
  Purchase #7 $190.34   7.421%   $204.4651   $204.47   $204.45   $204.50  
  7 purchase totals = $941.13       $1,033.5298   $1,033.53   $1,033.50   $1,033.50