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	$85.90	3.152%	$88.6076	$88.61	$88.60	$88.60
Purchase #2	$116.91	13.867%	$133.1219	$133.12	$133.10	$133.10
Purchase #3	$86.27	10.588%	$95.4043	$95.40	$95.40	$95.40
Purchase #4	$27.63	7.432%	$29.6835	$29.68	$29.70	$29.70
Purchase #5	$110.28	3.210%	$113.82	$113.82	$113.80	$113.80
Purchase #6	$221.65	3.521%	$229.4543	$229.45	$229.45	$229.50
Purchase #7	$86.54	3.689%	$89.7325	$89.73	$89.75	$89.70
7 purchase totals =	$735.18		$779.8241	$779.81	$779.80	$779.80