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	$67.82	9.536%	$74.2873	$74.29	$74.30	$74.30
Purchase #2	$80.66	11.151%	$89.6544	$89.65	$89.65	$89.70
Purchase #3	$55.63	6.793%	$59.4089	$59.41	$59.40	$59.40
Purchase #4	$205.54	3.415%	$212.5592	$212.56	$212.55	$212.60
Purchase #5	$118.71	13.134%	$134.3014	$134.30	$134.30	$134.30
Purchase #6	$136.56	9.747%	$149.8705	$149.87	$149.85	$149.90
Purchase #7	$231.39	10.271%	$255.1561	$255.16	$255.15	$255.20
7 purchase totals =	$896.31		$975.2378	$975.24	$975.20	$975.40