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 $249.64   7.591%   $268.5902   $268.59   $268.60   $268.60  
  Purchase #2 $236.42   6.568%   $251.9481   $251.95   $251.95   $251.90  
  Purchase #3 $61.26   8.207%   $66.2876   $66.29   $66.30   $66.30  
  Purchase #4 $121.36   8.609%   $131.8079   $131.81   $131.80   $131.80  
  Purchase #5 $118.95   3.676%   $123.3226   $123.32   $123.30   $123.30  
  Purchase #6 $226.68   8.106%   $245.0547   $245.05   $245.05   $245.10  
  Purchase #7 $115.27   10.742%   $127.6523   $127.65   $127.65   $127.70  
  7 purchase totals = $1,129.58       $1,214.6634   $1,214.66   $1,214.65   $1,214.70