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 $39.86   10.273%   $43.9548   $43.95   $43.95   $44.00  
  Purchase #2 $83.27   5.499%   $87.849   $87.85   $87.85   $87.80  
  Purchase #3 $119.70   12.444%   $134.5955   $134.60   $134.60   $134.60  
  Purchase #4 $191.99   11.865%   $214.7696   $214.77   $214.75   $214.80  
  Purchase #5 $166.63   3.859%   $173.0603   $173.06   $173.05   $173.10  
  Purchase #6 $13.60   3.285%   $14.0468   $14.05   $14.05   $14.00  
  Purchase #7 $169.31   4.264%   $176.5294   $176.53   $176.55   $176.50  
  7 purchase totals = $784.36       $844.8054   $844.81   $844.80   $844.80