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 $72.63   9.163%   $79.2851   $79.29   $79.30   $79.30  
  Purchase #2 $11.84   6.845%   $12.6504   $12.65   $12.65   $12.70  
  Purchase #3 $198.69   7.787%   $214.162   $214.16   $214.15   $214.20  
  Purchase #4 $75.47   5.863%   $79.8948   $79.89   $79.90   $79.90  
  Purchase #5 $89.95   7.448%   $96.6495   $96.65   $96.65   $96.60  
  Purchase #6 $223.82   13.417%   $253.8499   $253.85   $253.85   $253.80  
  Purchase #7 $202.29   11.274%   $225.0962   $225.10   $225.10   $225.10  
  7 purchase totals = $874.69       $961.5879   $961.59   $961.60   $961.60