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	$222.41	3.433%	$230.0453	$230.05	$230.05	$230.00
Purchase #2	$72.41	8.723%	$78.7263	$78.73	$78.75	$78.70
Purchase #3	$82.55	9.547%	$90.431	$90.43	$90.45	$90.40
Purchase #4	$141.56	12.344%	$159.0342	$159.03	$159.05	$159.00
Purchase #5	$174.82	6.475%	$186.1396	$186.14	$186.15	$186.10
Purchase #6	$194.50	12.816%	$219.4271	$219.43	$219.45	$219.40
Purchase #7	$32.53	7.542%	$34.9834	$34.98	$35.00	$35.00
7 purchase totals =	$920.78		$998.7869	$998.79	$998.90	$998.60