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	$29.53	5.275%	$31.0877	$31.09	$31.10	$31.10
Purchase #2	$96.30	9.110%	$105.0729	$105.07	$105.05	$105.10
Purchase #3	$27.71	9.762%	$30.4151	$30.42	$30.40	$30.40
Purchase #4	$244.56	7.838%	$263.7286	$263.73	$263.75	$263.70
Purchase #5	$57.90	3.109%	$59.7001	$59.70	$59.70	$59.70
Purchase #6	$84.50	8.224%	$91.4493	$91.45	$91.45	$91.40
Purchase #7	$58.79	13.845%	$66.9295	$66.93	$66.95	$66.90
7 purchase totals =	$599.29		$648.3832	$648.39	$648.40	$648.30