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 $216.80   11.259%   $241.2095   $241.21   $241.20   $241.20  
  Purchase #2 $144.73   8.456%   $156.9684   $156.97   $156.95   $157.00  
  Purchase #3 $36.49   5.513%   $38.5017   $38.50   $38.50   $38.50  
  Purchase #4 $195.52   12.533%   $220.0245   $220.02   $220.00   $220.00  
  Purchase #5 $229.38   4.267%   $239.1676   $239.17   $239.15   $239.20  
  Purchase #6 $93.38   3.450%   $96.6016   $96.60   $96.60   $96.60  
  Purchase #7 $52.57   13.707%   $59.7758   $59.78   $59.80   $59.80  
  7 purchase totals = $968.87       $1,052.2491   $1,052.25   $1,052.20   $1,052.30