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	$17.91	3.644%	$18.5626	$18.56	$18.55	$18.60
Purchase #2	$238.87	9.326%	$261.147	$261.15	$261.15	$261.10
Purchase #3	$177.70	5.194%	$186.9297	$186.93	$186.95	$186.90
Purchase #4	$79.54	12.448%	$89.4411	$89.44	$89.45	$89.40
Purchase #5	$82.90	13.518%	$94.1064	$94.11	$94.10	$94.10
Purchase #6	$143.56	6.175%	$152.4248	$152.42	$152.40	$152.40
Purchase #7	$230.55	5.666%	$243.613	$243.61	$243.60	$243.60
7 purchase totals =	$971.03		$1,046.2246	$1,046.22	$1,046.20	$1,046.10