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 $43.42   6.534%   $46.2571   $46.26   $46.25   $46.30  
  Purchase #2 $97.67   13.366%   $110.7246   $110.72   $110.70   $110.70  
  Purchase #3 $82.41   11.323%   $91.7413   $91.74   $91.75   $91.70  
  Purchase #4 $147.74   9.559%   $161.8625   $161.86   $161.85   $161.90  
  Purchase #5 $23.63   13.239%   $26.7584   $26.76   $26.75   $26.80  
  Purchase #6 $225.98   6.401%   $240.445   $240.45   $240.45   $240.40  
  Purchase #7 $39.38   13.210%   $44.5821   $44.58   $44.60   $44.60  
  7 purchase totals = $660.23       $722.3710   $722.37   $722.35   $722.40