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 $224.63   7.378%   $241.2032   $241.20   $241.20   $241.20  
  Purchase #2 $91.43   13.376%   $103.6597   $103.66   $103.65   $103.70  
  Purchase #3 $200.40   9.872%   $220.1835   $220.18   $220.20   $220.20  
  Purchase #4 $148.41   6.405%   $157.9157   $157.92   $157.90   $157.90  
  Purchase #5 $38.56   12.142%   $43.242   $43.24   $43.25   $43.20  
  Purchase #6 $94.90   9.595%   $104.0057   $104.01   $104.00   $104.00  
  Purchase #7 $13.61   10.537%   $15.0441   $15.04   $15.05   $15.00  
  7 purchase totals = $811.94       $885.2539   $885.25   $885.25   $885.20