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 $213.36   6.316%   $226.8358   $226.84   $226.85   $226.80  
  Purchase #2 $158.44   8.766%   $172.3289   $172.33   $172.35   $172.30  
  Purchase #3 $81.69   13.652%   $92.8423   $92.84   $92.85   $92.80  
  Purchase #4 $202.37   13.184%   $229.0505   $229.05   $229.05   $229.10  
  Purchase #5 $42.82   9.150%   $46.738   $46.74   $46.75   $46.70  
  Purchase #6 $244.35   9.611%   $267.8345   $267.83   $267.85   $267.80  
  Purchase #7 $182.88   4.593%   $191.2797   $191.28   $191.30   $191.30  
  7 purchase totals = $1,125.91       $1,226.9097   $1,226.91   $1,227.00   $1,226.80