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 $218.61   11.263%   $243.232   $243.23   $243.25   $243.20  
  Purchase #2 $169.64   3.133%   $174.9548   $174.95   $174.95   $175.00  
  Purchase #3 $221.54   11.546%   $247.119   $247.12   $247.10   $247.10  
  Purchase #4 $8.76   5.745%   $9.2633   $9.26   $9.25   $9.30  
  Purchase #5 $57.39   4.544%   $59.9978   $60.00   $60.00   $60.00  
  Purchase #6 $182.66   6.282%   $194.1347   $194.13   $194.15   $194.10  
  Purchase #7 $132.37   3.746%   $137.3286   $137.33   $137.35   $137.30  
  7 purchase totals = $990.97       $1,066.0302   $1,066.02   $1,066.05   $1,066.00