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 $57.52   6.244%   $61.1115   $61.11   $61.10   $61.10  
  Purchase #2 $237.38   5.434%   $250.2792   $250.28   $250.30   $250.30  
  Purchase #3 $34.92   4.661%   $36.5476   $36.55   $36.55   $36.50  
  Purchase #4 $133.93   13.406%   $151.8847   $151.88   $151.90   $151.90  
  Purchase #5 $209.53   3.564%   $216.9976   $217.00   $217.00   $217.00  
  Purchase #6 $186.54   4.134%   $194.2516   $194.25   $194.25   $194.30  
  Purchase #7 $39.30   9.311%   $42.9592   $42.96   $42.95   $43.00  
  7 purchase totals = $899.12       $954.0314   $954.03   $954.05   $954.10