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 $196.71   8.487%   $213.4048   $213.40   $213.40   $213.40  
  Purchase #2 $119.26   11.260%   $132.6887   $132.69   $132.70   $132.70  
  Purchase #3 $197.66   10.227%   $217.8747   $217.87   $217.85   $217.90  
  Purchase #4 $53.49   4.352%   $55.8179   $55.82   $55.80   $55.80  
  Purchase #5 $238.90   8.807%   $259.9399   $259.94   $259.95   $259.90  
  Purchase #6 $207.30   6.839%   $221.4772   $221.48   $221.50   $221.50  
  Purchase #7 $249.93   9.788%   $274.3931   $274.39   $274.40   $274.40  
  7 purchase totals = $1,263.25       $1,375.5963   $1,375.59   $1,375.60   $1,375.60