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	$178.63	6.606%	$190.4303	$190.43	$190.45	$190.40
Purchase #2	$133.78	8.417%	$145.0403	$145.04	$145.05	$145.00
Purchase #3	$71.42	9.676%	$78.3306	$78.33	$78.35	$78.30
Purchase #4	$132.82	12.756%	$149.7625	$149.76	$149.75	$149.80
Purchase #5	$185.65	11.486%	$206.9738	$206.97	$206.95	$207.00
Purchase #6	$156.71	3.784%	$162.6399	$162.64	$162.65	$162.60
Purchase #7	$224.92	13.665%	$255.6553	$255.66	$255.65	$255.70
7 purchase totals =	$1,083.93		$1,188.8327	$1,188.83	$1,188.85	$1,188.80