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 $237.95   6.762%   $254.0402   $254.04   $254.05   $254.00  
  Purchase #2 $156.59   6.806%   $167.2475   $167.25   $167.25   $167.20  
  Purchase #3 $250.75   8.641%   $272.4173   $272.42   $272.40   $272.40  
  Purchase #4 $248.63   10.344%   $274.3483   $274.35   $274.35   $274.30  
  Purchase #5 $186.65   9.148%   $203.7247   $203.72   $203.70   $203.70  
  Purchase #6 $199.58   6.756%   $213.0636   $213.06   $213.05   $213.10  
  Purchase #7 $170.31   9.677%   $186.7909   $186.79   $186.80   $186.80  
  7 purchase totals = $1,450.46       $1,571.6325   $1,571.63   $1,571.60   $1,571.50