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 $32.94   3.487%   $34.0886   $34.09   $34.10   $34.10  
  Purchase #2 $186.67   4.819%   $195.6656   $195.67   $195.65   $195.70  
  Purchase #3 $221.79   12.661%   $249.8708   $249.87   $249.85   $249.90  
  Purchase #4 $121.43   8.839%   $132.1632   $132.16   $132.15   $132.20  
  Purchase #5 $241.62   8.851%   $263.0058   $263.01   $263.00   $263.00  
  Purchase #6 $91.51   12.552%   $102.9963   $103.00   $103.00   $103.00  
  Purchase #7 $109.54   13.537%   $124.3684   $124.37   $124.35   $124.40  
  7 purchase totals = $1,005.50       $1,102.1587   $1,102.17   $1,102.10   $1,102.30