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 $33.84   3.151%   $34.9063   $34.91   $34.90   $34.90  
  Purchase #2 $196.82   4.659%   $205.9898   $205.99   $206.00   $206.00  
  Purchase #3 $95.64   3.839%   $99.3116   $99.31   $99.30   $99.30  
  Purchase #4 $215.29   12.838%   $242.9289   $242.93   $242.95   $242.90  
  Purchase #5 $130.80   8.169%   $141.4851   $141.49   $141.50   $141.50  
  Purchase #6 $15.94   4.705%   $16.69   $16.69   $16.70   $16.70  
  Purchase #7 $112.43   3.471%   $116.3324   $116.33   $116.35   $116.30  
  7 purchase totals = $800.76       $857.6441   $857.65   $857.70   $857.60