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 $83.75   13.368%   $94.9457   $94.95   $94.95   $94.90  
  Purchase #2 $161.70   3.602%   $167.5244   $167.52   $167.50   $167.50  
  Purchase #3 $152.61   6.535%   $162.5831   $162.58   $162.60   $162.60  
  Purchase #4 $198.65   5.194%   $208.9679   $208.97   $208.95   $209.00  
  Purchase #5 $36.95   12.364%   $41.5185   $41.52   $41.50   $41.50  
  Purchase #6 $217.97   10.788%   $241.4846   $241.48   $241.50   $241.50  
  Purchase #7 $77.58   6.610%   $82.708   $82.71   $82.70   $82.70  
  7 purchase totals = $929.21       $999.7322   $999.73   $999.70   $999.70