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	$125.74	6.805%	$134.2966	$134.30	$134.30	$134.30
Purchase #2	$103.92	4.497%	$108.5933	$108.59	$108.60	$108.60
Purchase #3	$119.85	6.103%	$127.1644	$127.16	$127.15	$127.20
Purchase #4	$105.58	9.629%	$115.7463	$115.75	$115.75	$115.70
Purchase #5	$207.76	7.308%	$222.9431	$222.94	$222.95	$222.90
Purchase #6	$69.56	12.507%	$78.2599	$78.26	$78.25	$78.30
Purchase #7	$66.47	11.227%	$73.9326	$73.93	$73.95	$73.90
7 purchase totals =	$798.88		$860.9362	$860.93	$860.95	$860.90