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	$93.75	4.866%	$98.3119	$98.31	$98.30	$98.30
Purchase #2	$104.75	8.179%	$113.3175	$113.32	$113.30	$113.30
Purchase #3	$86.48	4.846%	$90.6708	$90.67	$90.65	$90.70
Purchase #4	$117.56	10.378%	$129.7604	$129.76	$129.75	$129.80
Purchase #5	$105.65	8.230%	$114.345	$114.35	$114.35	$114.30
Purchase #6	$107.65	8.240%	$116.5204	$116.52	$116.50	$116.50
Purchase #7	$239.93	6.400%	$255.2855	$255.29	$255.30	$255.30
7 purchase totals =	$855.77		$918.2115	$918.22	$918.15	$918.20