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 $62.79   6.566%   $66.9128   $66.91   $66.90   $66.90  
  Purchase #2 $87.73   9.762%   $96.2942   $96.29   $96.30   $96.30  
  Purchase #3 $112.66   6.869%   $120.3986   $120.40   $120.40   $120.40  
  Purchase #4 $248.38   9.746%   $272.5871   $272.59   $272.60   $272.60  
  Purchase #5 $177.42   12.562%   $199.7075   $199.71   $199.70   $199.70  
  Purchase #6 $242.62   6.231%   $257.7377   $257.74   $257.75   $257.70  
  Purchase #7 $241.66   6.554%   $257.4984   $257.50   $257.50   $257.50  
  7 purchase totals = $1,173.26       $1,271.1363   $1,271.14   $1,271.15   $1,271.10