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	$20.72	4.624%	$21.6781	$21.68	$21.70	$21.70
Purchase #2	$81.83	13.580%	$92.9425	$92.94	$92.95	$92.90
Purchase #3	$165.48	4.489%	$172.9084	$172.91	$172.90	$172.90
Purchase #4	$101.36	11.755%	$113.2749	$113.27	$113.25	$113.30
Purchase #5	$87.58	4.826%	$91.8066	$91.81	$91.80	$91.80
Purchase #6	$151.66	7.403%	$162.8874	$162.89	$162.90	$162.90
Purchase #7	$151.31	8.560%	$164.2621	$164.26	$164.25	$164.30
7 purchase totals =	$759.94		$819.7600	$819.76	$819.75	$819.80