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	$230.31	3.265%	$237.8296	$237.83	$237.85	$237.80
Purchase #2	$28.78	6.708%	$30.7106	$30.71	$30.70	$30.70
Purchase #3	$149.35	11.639%	$166.7328	$166.73	$166.75	$166.70
Purchase #4	$192.91	13.413%	$218.785	$218.79	$218.80	$218.80
Purchase #5	$86.28	4.182%	$89.8882	$89.89	$89.90	$89.90
Purchase #6	$147.72	7.237%	$158.4105	$158.41	$158.40	$158.40
Purchase #7	$64.86	10.414%	$71.6145	$71.61	$71.60	$71.60
7 purchase totals =	$900.21		$973.9712	$973.97	$974.00	$973.90