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	$220.83	13.564%	$250.7834	$250.78	$250.80	$250.80
Purchase #2	$14.82	4.215%	$15.4447	$15.44	$15.45	$15.40
Purchase #3	$182.27	7.493%	$195.9275	$195.93	$195.95	$195.90
Purchase #4	$43.56	5.171%	$45.8125	$45.81	$45.80	$45.80
Purchase #5	$48.57	11.204%	$54.0118	$54.01	$54.00	$54.00
Purchase #6	$133.82	5.147%	$140.7077	$140.71	$140.70	$140.70
Purchase #7	$35.67	9.736%	$39.1428	$39.14	$39.15	$39.10
7 purchase totals =	$679.54		$741.8304	$741.82	$741.85	$741.70