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 $41.95   6.701%   $44.7611   $44.76   $44.75   $44.80  
  Purchase #2 $9.26   4.451%   $9.6722   $9.67   $9.65   $9.70  
  Purchase #3 $73.47   5.488%   $77.502   $77.50   $77.50   $77.50  
  Purchase #4 $129.28   3.369%   $133.6354   $133.64   $133.65   $133.60  
  Purchase #5 $191.58   3.355%   $198.0075   $198.01   $198.00   $198.00  
  Purchase #6 $180.25   3.140%   $185.9099   $185.91   $185.90   $185.90  
  Purchase #7 $128.63   13.703%   $146.2562   $146.26   $146.25   $146.30  
  7 purchase totals = $754.42       $795.7443   $795.75   $795.70   $795.80