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 $107.76   13.726%   $122.5511   $122.55   $122.55   $122.60  
  Purchase #2 $232.31   13.148%   $262.8541   $262.85   $262.85   $262.90  
  Purchase #3 $237.86   12.195%   $266.867   $266.87   $266.85   $266.90  
  Purchase #4 $144.36   11.861%   $161.4825   $161.48   $161.50   $161.50  
  Purchase #5 $136.60   6.446%   $145.4052   $145.41   $145.40   $145.40  
  Purchase #6 $121.42   12.236%   $136.277   $136.28   $136.30   $136.30  
  Purchase #7 $85.40   12.145%   $95.7718   $95.77   $95.75   $95.80  
  7 purchase totals = $1,065.71       $1,191.2087   $1,191.21   $1,191.20   $1,191.40