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 $205.76   11.285%   $228.98   $228.98   $229.00   $229.00  
  Purchase #2 $22.80   6.406%   $24.2606   $24.26   $24.25   $24.30  
  Purchase #3 $155.85   8.738%   $169.4682   $169.47   $169.45   $169.50  
  Purchase #4 $198.52   13.303%   $224.9291   $224.93   $224.95   $224.90  
  Purchase #5 $17.25   9.130%   $18.8249   $18.82   $18.80   $18.80  
  Purchase #6 $94.63   3.576%   $98.014   $98.01   $98.00   $98.00  
  Purchase #7 $141.47   13.267%   $160.2388   $160.24   $160.25   $160.20  
  7 purchase totals = $836.28       $924.7156   $924.71   $924.70   $924.70