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	$92.34	7.381%	$99.1556	$99.16	$99.15	$99.20
Purchase #2	$110.96	11.538%	$123.7626	$123.76	$123.75	$123.80
Purchase #3	$172.79	11.475%	$192.6177	$192.62	$192.60	$192.60
Purchase #4	$181.44	5.183%	$190.844	$190.84	$190.85	$190.80
Purchase #5	$80.31	10.254%	$88.545	$88.55	$88.55	$88.50
Purchase #6	$35.35	11.273%	$39.335	$39.34	$39.35	$39.30
Purchase #7	$140.51	13.378%	$159.3074	$159.31	$159.30	$159.30
7 purchase totals =	$813.70		$893.5673	$893.58	$893.55	$893.50