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 $100.70   11.539%   $112.3198   $112.32   $112.30   $112.30  
  Purchase #2 $242.39   3.355%   $250.5222   $250.52   $250.50   $250.50  
  Purchase #3 $149.38   4.567%   $156.2022   $156.20   $156.20   $156.20  
  Purchase #4 $19.37   4.438%   $20.2296   $20.23   $20.25   $20.20  
  Purchase #5 $59.31   9.602%   $65.0049   $65.00   $65.00   $65.00  
  Purchase #6 $191.91   13.590%   $217.9906   $217.99   $218.00   $218.00  
  Purchase #7 $58.44   6.650%   $62.3263   $62.33   $62.35   $62.30  
  7 purchase totals = $821.50       $884.5956   $884.59   $884.60   $884.50