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 $64.82   3.291%   $66.9532   $66.95   $66.95   $67.00  
  Purchase #2 $233.89   3.703%   $242.5509   $242.55   $242.55   $242.60  
  Purchase #3 $160.33   5.361%   $168.9253   $168.93   $168.95   $168.90  
  Purchase #4 $177.85   8.795%   $193.4919   $193.49   $193.50   $193.50  
  Purchase #5 $236.51   8.405%   $256.3887   $256.39   $256.40   $256.40  
  Purchase #6 $159.41   12.175%   $178.8182   $178.82   $178.80   $178.80  
  Purchase #7 $211.60   13.350%   $239.8486   $239.85   $239.85   $239.80  
  7 purchase totals = $1,244.41       $1,346.9768   $1,346.98   $1,347.00   $1,347.00