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 $60.79   5.108%   $63.8952   $63.90   $63.90   $63.90  
  Purchase #2 $210.83   13.375%   $239.0285   $239.03   $239.05   $239.00  
  Purchase #3 $244.86   9.397%   $267.8695   $267.87   $267.85   $267.90  
  Purchase #4 $232.69   13.182%   $263.3632   $263.36   $263.35   $263.40  
  Purchase #5 $205.49   4.167%   $214.0528   $214.05   $214.05   $214.10  
  Purchase #6 $250.69   9.774%   $275.1924   $275.19   $275.20   $275.20  
  Purchase #7 $194.49   8.227%   $210.4907   $210.49   $210.50   $210.50  
  7 purchase totals = $1,399.84       $1,533.8923   $1,533.89   $1,533.90   $1,534.00