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 $219.41   10.185%   $241.7569   $241.76   $241.75   $241.80  
  Purchase #2 $53.99   13.549%   $61.3051   $61.31   $61.30   $61.30  
  Purchase #3 $204.99   11.111%   $227.7664   $227.77   $227.75   $227.80  
  Purchase #4 $239.90   7.807%   $258.629   $258.63   $258.65   $258.60  
  Purchase #5 $146.97   9.787%   $161.354   $161.35   $161.35   $161.40  
  Purchase #6 $123.49   11.852%   $138.126   $138.13   $138.15   $138.10  
  Purchase #7 $169.97   9.155%   $185.5308   $185.53   $185.55   $185.50  
  7 purchase totals = $1,158.72       $1,274.4682   $1,274.48   $1,274.50   $1,274.50