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	$54.28	9.188%	$59.2672	$59.27	$59.25	$59.30
Purchase #2	$217.31	12.702%	$244.9127	$244.91	$244.90	$244.90
Purchase #3	$170.31	6.570%	$181.4994	$181.50	$181.50	$181.50
Purchase #4	$158.53	13.437%	$179.8317	$179.83	$179.85	$179.80
Purchase #5	$148.78	7.313%	$159.6603	$159.66	$159.65	$159.70
Purchase #6	$218.86	5.554%	$231.0155	$231.02	$231.00	$231.00
Purchase #7	$175.60	7.720%	$189.1563	$189.16	$189.15	$189.20
7 purchase totals =	$1,143.67		$1,245.3431	$1,245.35	$1,245.30	$1,245.40