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	$44.33	9.294%	$48.45	$48.45	$48.45	$48.50
Purchase #2	$97.42	8.689%	$105.8848	$105.88	$105.90	$105.90
Purchase #3	$223.47	13.460%	$253.5491	$253.55	$253.55	$253.50
Purchase #4	$248.68	6.465%	$264.7572	$264.76	$264.75	$264.80
Purchase #5	$168.90	6.633%	$180.1031	$180.10	$180.10	$180.10
Purchase #6	$37.33	11.191%	$41.5076	$41.51	$41.50	$41.50
Purchase #7	$223.65	5.242%	$235.3737	$235.37	$235.35	$235.40
7 purchase totals =	$1,043.78		$1,129.6255	$1,129.62	$1,129.60	$1,129.70