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	$91.32	5.668%	$96.496	$96.50	$96.50	$96.50
Purchase #2	$18.71	9.367%	$20.4626	$20.46	$20.45	$20.50
Purchase #3	$26.53	11.725%	$29.6406	$29.64	$29.65	$29.60
Purchase #4	$99.48	8.658%	$108.093	$108.09	$108.10	$108.10
Purchase #5	$88.35	12.647%	$99.5236	$99.52	$99.50	$99.50
Purchase #6	$93.53	13.446%	$106.106	$106.11	$106.10	$106.10
Purchase #7	$41.31	3.695%	$42.8364	$42.84	$42.85	$42.80
7 purchase totals =	$459.23		$503.1582	$503.16	$503.15	$503.10