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	$73.58	13.168%	$83.269	$83.27	$83.25	$83.30
Purchase #2	$37.67	11.832%	$42.1271	$42.13	$42.15	$42.10
Purchase #3	$85.63	8.515%	$92.9214	$92.92	$92.90	$92.90
Purchase #4	$159.91	8.603%	$173.6671	$173.67	$173.65	$173.70
Purchase #5	$129.60	4.606%	$135.5694	$135.57	$135.55	$135.60
Purchase #6	$102.94	12.841%	$116.1585	$116.16	$116.15	$116.20
Purchase #7	$118.59	7.586%	$127.5862	$127.59	$127.60	$127.60
7 purchase totals =	$707.92		$771.2987	$771.31	$771.25	$771.40