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 $219.98   10.243%   $242.5126   $242.51   $242.50   $242.50  
  Purchase #2 $136.79   10.797%   $151.5592   $151.56   $151.55   $151.60  
  Purchase #3 $215.49   12.188%   $241.7539   $241.75   $241.75   $241.80  
  Purchase #4 $216.81   4.245%   $226.0136   $226.01   $226.00   $226.00  
  Purchase #5 $36.26   5.597%   $38.2895   $38.29   $38.30   $38.30  
  Purchase #6 $202.77   12.243%   $227.5951   $227.60   $227.60   $227.60  
  Purchase #7 $196.76   4.430%   $205.4765   $205.48   $205.50   $205.50  
  7 purchase totals = $1,224.86       $1,333.2004   $1,333.20   $1,333.20   $1,333.30