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	$10.85	8.205%	$11.7402	$11.74	$11.75	$11.70
Purchase #2	$61.30	13.870%	$69.8023	$69.80	$69.80	$69.80
Purchase #3	$203.84	9.801%	$223.8184	$223.82	$223.80	$223.80
Purchase #4	$79.88	12.443%	$89.8195	$89.82	$89.80	$89.80
Purchase #5	$85.49	10.495%	$94.4622	$94.46	$94.45	$94.50
Purchase #6	$18.54	9.323%	$20.2685	$20.27	$20.25	$20.30
Purchase #7	$53.69	12.506%	$60.4045	$60.40	$60.40	$60.40
7 purchase totals =	$513.59		$570.3156	$570.31	$570.25	$570.30