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 $64.86   6.582%   $69.1291   $69.13   $69.15   $69.10  
  Purchase #2 $154.70   6.526%   $164.7957   $164.80   $164.80   $164.80  
  Purchase #3 $85.59   11.352%   $95.3062   $95.31   $95.30   $95.30  
  Purchase #4 $70.92   8.187%   $76.7262   $76.73   $76.75   $76.70  
  Purchase #5 $229.67   8.667%   $249.5755   $249.58   $249.60   $249.60  
  Purchase #6 $159.70   8.626%   $173.4757   $173.48   $173.50   $173.50  
  Purchase #7 $248.99   9.223%   $271.9543   $271.95   $271.95   $272.00  
  7 purchase totals = $1,014.43       $1,100.9627   $1,100.98   $1,101.05   $1,101.00