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	$52.28	5.634%	$55.2255	$55.23	$55.25	$55.20
Purchase #2	$161.59	4.798%	$169.3431	$169.34	$169.35	$169.30
Purchase #3	$94.63	9.273%	$103.405	$103.41	$103.40	$103.40
Purchase #4	$29.62	12.259%	$33.2511	$33.25	$33.25	$33.30
Purchase #5	$91.69	4.172%	$95.5153	$95.52	$95.50	$95.50
Purchase #6	$197.52	13.580%	$224.3432	$224.34	$224.35	$224.30
Purchase #7	$41.28	11.833%	$46.1647	$46.16	$46.15	$46.20
7 purchase totals =	$668.61		$727.2479	$727.25	$727.25	$727.20