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	$156.48	12.846%	$176.5814	$176.58	$176.60	$176.60
Purchase #2	$104.65	7.614%	$112.6181	$112.62	$112.60	$112.60
Purchase #3	$49.93	10.872%	$55.3584	$55.36	$55.35	$55.40
Purchase #4	$240.90	13.561%	$273.5684	$273.57	$273.55	$273.60
Purchase #5	$61.71	6.312%	$65.6051	$65.61	$65.60	$65.60
Purchase #6	$53.78	7.372%	$57.7447	$57.74	$57.75	$57.70
Purchase #7	$130.41	9.292%	$142.5277	$142.53	$142.55	$142.50
7 purchase totals =	$797.86		$884.0038	$884.01	$884.00	$884.00