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 $218.65   3.247%   $225.7496   $225.75   $225.75   $225.70  
  Purchase #2 $241.83   6.519%   $257.5949   $257.59   $257.60   $257.60  
  Purchase #3 $179.93   6.202%   $191.0893   $191.09   $191.10   $191.10  
  Purchase #4 $237.88   8.813%   $258.8444   $258.84   $258.85   $258.80  
  Purchase #5 $167.70   4.112%   $174.5958   $174.60   $174.60   $174.60  
  Purchase #6 $167.85   7.726%   $180.8181   $180.82   $180.80   $180.80  
  Purchase #7 $231.41   10.448%   $255.5877   $255.59   $255.60   $255.60  
  7 purchase totals = $1,445.25       $1,544.2798   $1,544.28   $1,544.30   $1,544.20