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 $62.97   12.732%   $70.9873   $70.99   $71.00   $71.00  
  Purchase #2 $224.34   6.805%   $239.6063   $239.61   $239.60   $239.60  
  Purchase #3 $59.77   8.535%   $64.8714   $64.87   $64.85   $64.90  
  Purchase #4 $63.84   5.249%   $67.191   $67.19   $67.20   $67.20  
  Purchase #5 $164.95   10.562%   $182.372   $182.37   $182.35   $182.40  
  Purchase #6 $59.30   9.594%   $64.9892   $64.99   $65.00   $65.00  
  Purchase #7 $37.38   8.301%   $40.4829   $40.48   $40.50   $40.50  
  7 purchase totals = $672.55       $730.5001   $730.50   $730.50   $730.60