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 $99.86   6.205%   $106.0563   $106.06   $106.05   $106.10  
  Purchase #2 $178.86   9.576%   $195.9876   $195.99   $196.00   $196.00  
  Purchase #3 $43.83   13.864%   $49.9066   $49.91   $49.90   $49.90  
  Purchase #4 $161.84   5.463%   $170.6813   $170.68   $170.70   $170.70  
  Purchase #5 $164.72   6.805%   $175.9292   $175.93   $175.95   $175.90  
  Purchase #6 $231.26   7.236%   $247.994   $247.99   $248.00   $248.00  
  Purchase #7 $5.99   5.286%   $6.3066   $6.31   $6.30   $6.30  
  7 purchase totals = $886.36       $952.8616   $952.87   $952.90   $952.90