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	$214.85	11.501%	$239.5599	$239.56	$239.55	$239.60
Purchase #2	$169.84	9.250%	$185.5502	$185.55	$185.55	$185.60
Purchase #3	$92.72	4.633%	$97.0157	$97.02	$97.00	$97.00
Purchase #4	$38.50	4.272%	$40.1447	$40.14	$40.15	$40.10
Purchase #5	$39.93	13.120%	$45.1688	$45.17	$45.15	$45.20
Purchase #6	$127.73	7.692%	$137.555	$137.56	$137.55	$137.60
Purchase #7	$32.27	5.530%	$34.0545	$34.05	$34.05	$34.10
7 purchase totals =	$715.84		$779.0488	$779.05	$779.00	$779.20