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 $57.27   12.831%   $64.6183   $64.62   $64.60   $64.60  
  Purchase #2 $125.91   13.239%   $142.5792   $142.58   $142.60   $142.60  
  Purchase #3 $107.35   8.844%   $116.844   $116.84   $116.85   $116.80  
  Purchase #4 $112.34   10.867%   $124.548   $124.55   $124.55   $124.50  
  Purchase #5 $170.57   5.187%   $179.4175   $179.42   $179.40   $179.40  
  Purchase #6 $20.58   5.392%   $21.6897   $21.69   $21.70   $21.70  
  Purchase #7 $77.33   8.439%   $83.8559   $83.86   $83.85   $83.90  
  7 purchase totals = $671.35       $733.5526   $733.56   $733.55   $733.50