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   10.610%   $66.7753   $66.78   $66.80   $66.80  
  Purchase #2 $238.40   5.671%   $251.9197   $251.92   $251.90   $251.90  
  Purchase #3 $250.66   13.636%   $284.84   $284.84   $284.85   $284.80  
  Purchase #4 $118.38   12.607%   $133.3042   $133.30   $133.30   $133.30  
  Purchase #5 $50.96   9.644%   $55.8746   $55.87   $55.85   $55.90  
  Purchase #6 $192.93   6.312%   $205.1077   $205.11   $205.10   $205.10  
  Purchase #7 $243.96   7.184%   $261.4861   $261.49   $261.50   $261.50  
  7 purchase totals = $1,155.66       $1,259.3076   $1,259.31   $1,259.30   $1,259.30