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 $55.75   12.333%   $62.6256   $62.63   $62.65   $62.60  
  Purchase #2 $95.58   12.850%   $107.862   $107.86   $107.85   $107.90  
  Purchase #3 $168.50   10.136%   $185.5792   $185.58   $185.60   $185.60  
  Purchase #4 $186.91   9.657%   $204.9599   $204.96   $204.95   $205.00  
  Purchase #5 $65.71   10.863%   $72.8481   $72.85   $72.85   $72.80  
  Purchase #6 $60.62   4.296%   $63.2242   $63.22   $63.20   $63.20  
  Purchase #7 $23.77   9.207%   $25.9585   $25.96   $25.95   $26.00  
  7 purchase totals = $656.84       $723.0575   $723.06   $723.05   $723.10