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 $94.99   10.549%   $105.0105   $105.01   $105.00   $105.00  
  Purchase #2 $141.68   3.725%   $146.9576   $146.96   $146.95   $147.00  
  Purchase #3 $69.95   4.183%   $72.876   $72.88   $72.90   $72.90  
  Purchase #4 $94.80   13.225%   $107.3373   $107.34   $107.35   $107.30  
  Purchase #5 $129.97   5.355%   $136.9299   $136.93   $136.95   $136.90  
  Purchase #6 $134.93   8.311%   $146.144   $146.14   $146.15   $146.10  
  Purchase #7 $188.95   9.304%   $206.5299   $206.53   $206.55   $206.50  
  7 purchase totals = $855.27       $921.7852   $921.79   $921.85   $921.70