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 $62.76   6.279%   $66.7007   $66.70   $66.70   $66.70  
  Purchase #2 $223.39   13.551%   $253.6616   $253.66   $253.65   $253.70  
  Purchase #3 $181.45   10.558%   $200.6075   $200.61   $200.60   $200.60  
  Purchase #4 $196.64   12.321%   $220.868   $220.87   $220.85   $220.90  
  Purchase #5 $221.86   11.164%   $246.6285   $246.63   $246.65   $246.60  
  Purchase #6 $168.75   8.536%   $183.1545   $183.15   $183.15   $183.20  
  Purchase #7 $86.83   5.865%   $91.9226   $91.92   $91.90   $91.90  
  7 purchase totals = $1,141.68       $1,263.5434   $1,263.54   $1,263.50   $1,263.60