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 $74.38   10.261%   $82.0121   $82.01   $82.00   $82.00  
  Purchase #2 $242.69   5.299%   $255.5501   $255.55   $255.55   $255.60  
  Purchase #3 $112.52   12.436%   $126.513   $126.51   $126.50   $126.50  
  Purchase #4 $204.44   7.501%   $219.775   $219.78   $219.80   $219.80  
  Purchase #5 $184.46   11.642%   $205.9348   $205.93   $205.95   $205.90  
  Purchase #6 $178.55   9.207%   $194.9891   $194.99   $195.00   $195.00  
  Purchase #7 $124.25   6.550%   $132.3884   $132.39   $132.40   $132.40  
  7 purchase totals = $1,121.29       $1,217.1625   $1,217.16   $1,217.20   $1,217.20