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 $224.98   8.716%   $244.5893   $244.59   $244.60   $244.60  
  Purchase #2 $166.99   9.487%   $182.8323   $182.83   $182.85   $182.80  
  Purchase #3 $186.41   8.635%   $202.5065   $202.51   $202.50   $202.50  
  Purchase #4 $5.98   12.166%   $6.7075   $6.71   $6.70   $6.70  
  Purchase #5 $237.54   9.306%   $259.6455   $259.65   $259.65   $259.60  
  Purchase #6 $209.86   5.604%   $221.6206   $221.62   $221.60   $221.60  
  Purchase #7 $105.55   3.109%   $108.8315   $108.83   $108.85   $108.80  
  7 purchase totals = $1,137.31       $1,226.7332   $1,226.74   $1,226.75   $1,226.60