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	$96.53	3.498%	$99.9066	$99.91	$99.90	$99.90
Purchase #2	$107.73	3.647%	$111.6589	$111.66	$111.65	$111.70
Purchase #3	$158.75	4.485%	$165.8699	$165.87	$165.85	$165.90
Purchase #4	$209.75	13.494%	$238.0537	$238.05	$238.05	$238.10
Purchase #5	$85.35	11.570%	$95.225	$95.23	$95.25	$95.20
Purchase #6	$122.41	5.253%	$128.8402	$128.84	$128.85	$128.80
Purchase #7	$126.28	4.455%	$131.9058	$131.91	$131.90	$131.90
7 purchase totals =	$906.80		$971.4601	$971.47	$971.45	$971.50