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 $60.37   5.745%   $63.8383   $63.84   $63.85   $63.80  
  Purchase #2 $135.59   13.458%   $153.8377   $153.84   $153.85   $153.80  
  Purchase #3 $7.96   4.239%   $8.2974   $8.30   $8.30   $8.30  
  Purchase #4 $175.85   11.239%   $195.6138   $195.61   $195.60   $195.60  
  Purchase #5 $59.92   7.455%   $64.387   $64.39   $64.40   $64.40  
  Purchase #6 $246.97   7.610%   $265.7644   $265.76   $265.75   $265.80  
  Purchase #7 $39.86   12.227%   $44.7337   $44.73   $44.75   $44.70  
  7 purchase totals = $726.52       $796.4723   $796.47   $796.50   $796.40