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 $244.67   6.247%   $259.9545   $259.95   $259.95   $260.00  
  Purchase #2 $215.47   9.865%   $236.7261   $236.73   $236.75   $236.70  
  Purchase #3 $14.47   6.473%   $15.4066   $15.41   $15.40   $15.40  
  Purchase #4 $156.55   8.355%   $169.6298   $169.63   $169.65   $169.60  
  Purchase #5 $159.88   13.532%   $181.515   $181.52   $181.50   $181.50  
  Purchase #6 $171.32   10.122%   $188.661   $188.66   $188.65   $188.70  
  Purchase #7 $164.46   10.457%   $181.6576   $181.66   $181.65   $181.70  
  7 purchase totals = $1,126.82       $1,233.5506   $1,233.56   $1,233.55   $1,233.60