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 $182.36   11.756%   $203.7982   $203.80   $203.80   $203.80  
  Purchase #2 $83.66   12.376%   $94.0138   $94.01   $94.00   $94.00  
  Purchase #3 $108.76   4.455%   $113.6053   $113.61   $113.60   $113.60  
  Purchase #4 $187.77   10.632%   $207.7337   $207.73   $207.75   $207.70  
  Purchase #5 $8.85   6.728%   $9.4454   $9.45   $9.45   $9.40  
  Purchase #6 $146.63   10.479%   $161.9954   $162.00   $162.00   $162.00  
  Purchase #7 $165.37   3.824%   $171.6937   $171.69   $171.70   $171.70  
  7 purchase totals = $883.40       $962.2855   $962.29   $962.30   $962.20