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	$110.25	3.667%	$114.2929	$114.29	$114.30	$114.30
Purchase #2	$12.55	4.612%	$13.1288	$13.13	$13.15	$13.10
Purchase #3	$151.62	3.386%	$156.7539	$156.75	$156.75	$156.80
Purchase #4	$149.51	4.614%	$156.4084	$156.41	$156.40	$156.40
Purchase #5	$173.59	5.869%	$183.778	$183.78	$183.80	$183.80
Purchase #6	$68.90	13.374%	$78.1147	$78.11	$78.10	$78.10
Purchase #7	$131.98	5.440%	$139.1597	$139.16	$139.15	$139.20
7 purchase totals =	$798.40		$841.6364	$841.63	$841.65	$841.70