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	$100.35	9.119%	$109.5009	$109.50	$109.50	$109.50
Purchase #2	$165.70	11.832%	$185.3056	$185.31	$185.30	$185.30
Purchase #3	$217.85	11.698%	$243.3341	$243.33	$243.35	$243.30
Purchase #4	$33.27	10.110%	$36.6336	$36.63	$36.65	$36.60
Purchase #5	$79.44	3.313%	$82.0718	$82.07	$82.05	$82.10
Purchase #6	$238.48	10.169%	$262.731	$262.73	$262.75	$262.70
Purchase #7	$225.76	13.247%	$255.6664	$255.67	$255.65	$255.70
7 purchase totals =	$1,060.85		$1,175.2434	$1,175.24	$1,175.25	$1,175.20