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 $65.33   11.772%   $73.0206   $73.02   $73.00   $73.00  
  Purchase #2 $41.68   12.386%   $46.8425   $46.84   $46.85   $46.80  
  Purchase #3 $202.52   9.413%   $221.5832   $221.58   $221.60   $221.60  
  Purchase #4 $93.76   5.388%   $98.8118   $98.81   $98.80   $98.80  
  Purchase #5 $226.96   10.258%   $250.2416   $250.24   $250.25   $250.20  
  Purchase #6 $39.39   12.527%   $44.3244   $44.32   $44.30   $44.30  
  Purchase #7 $161.93   12.856%   $182.7477   $182.75   $182.75   $182.70  
  7 purchase totals = $831.57       $917.5718   $917.56   $917.55   $917.40