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 $32.72   5.791%   $34.6148   $34.61   $34.60   $34.60  
  Purchase #2 $124.74   6.191%   $132.4627   $132.46   $132.45   $132.50  
  Purchase #3 $219.72   8.171%   $237.6733   $237.67   $237.65   $237.70  
  Purchase #4 $134.32   10.843%   $148.8843   $148.88   $148.90   $148.90  
  Purchase #5 $87.84   7.385%   $94.327   $94.33   $94.35   $94.30  
  Purchase #6 $233.40   12.186%   $261.8421   $261.84   $261.85   $261.80  
  Purchase #7 $86.50   11.175%   $96.1664   $96.17   $96.15   $96.20  
  7 purchase totals = $919.24       $1,005.9706   $1,005.96   $1,005.95   $1,006.00