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 $21.35   4.355%   $22.2798   $22.28   $22.30   $22.30  
  Purchase #2 $111.32   5.177%   $117.083   $117.08   $117.10   $117.10  
  Purchase #3 $240.47   13.276%   $272.3948   $272.39   $272.40   $272.40  
  Purchase #4 $53.84   11.308%   $59.9282   $59.93   $59.95   $59.90  
  Purchase #5 $100.43   12.467%   $112.9506   $112.95   $112.95   $113.00  
  Purchase #6 $157.32   8.122%   $170.0975   $170.10   $170.10   $170.10  
  Purchase #7 $146.99   8.473%   $159.4445   $159.44   $159.45   $159.40  
  7 purchase totals = $831.72       $914.1784   $914.17   $914.25   $914.20