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	$229.65	11.529%	$256.1263	$256.13	$256.15	$256.10
Purchase #2	$229.87	8.171%	$248.6527	$248.65	$248.65	$248.70
Purchase #3	$85.79	5.707%	$90.686	$90.69	$90.70	$90.70
Purchase #4	$127.62	5.641%	$134.819	$134.82	$134.80	$134.80
Purchase #5	$85.35	6.412%	$90.8226	$90.82	$90.80	$90.80
Purchase #6	$123.87	6.415%	$131.8163	$131.82	$131.80	$131.80
Purchase #7	$27.76	7.779%	$29.9195	$29.92	$29.90	$29.90
7 purchase totals =	$909.91		$982.8424	$982.85	$982.80	$982.80