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 $62.75   8.590%   $68.1402   $68.14   $68.15   $68.10  
  Purchase #2 $185.74   7.122%   $198.9684   $198.97   $198.95   $199.00  
  Purchase #3 $242.69   13.607%   $275.7128   $275.71   $275.70   $275.70  
  Purchase #4 $173.44   10.295%   $191.2956   $191.30   $191.30   $191.30  
  Purchase #5 $151.32   3.222%   $156.1955   $156.20   $156.20   $156.20  
  Purchase #6 $197.73   5.727%   $209.054   $209.05   $209.05   $209.10  
  Purchase #7 $105.92   10.326%   $116.8573   $116.86   $116.85   $116.90  
  7 purchase totals = $1,119.59       $1,216.2238   $1,216.23   $1,216.20   $1,216.30