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 $195.66   8.158%   $211.6219   $211.62   $211.60   $211.60  
  Purchase #2 $153.77   13.136%   $173.9692   $173.97   $173.95   $174.00  
  Purchase #3 $52.48   4.404%   $54.7912   $54.79   $54.80   $54.80  
  Purchase #4 $191.32   6.365%   $203.4975   $203.50   $203.50   $203.50  
  Purchase #5 $76.42   7.312%   $82.0078   $82.01   $82.00   $82.00  
  Purchase #6 $45.89   3.565%   $47.526   $47.53   $47.55   $47.50  
  Purchase #7 $208.60   5.567%   $220.2128   $220.21   $220.20   $220.20  
  7 purchase totals = $924.14       $993.6264   $993.63   $993.60   $993.60