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	$80.39	11.632%	$89.741	$89.74	$89.75	$89.70
Purchase #2	$62.95	4.118%	$65.5423	$65.54	$65.55	$65.50
Purchase #3	$136.32	5.386%	$143.6622	$143.66	$143.65	$143.70
Purchase #4	$212.34	9.174%	$231.8201	$231.82	$231.80	$231.80
Purchase #5	$219.34	5.380%	$231.1405	$231.14	$231.15	$231.10
Purchase #6	$63.86	5.251%	$67.2133	$67.21	$67.20	$67.20
Purchase #7	$66.78	12.335%	$75.0173	$75.02	$75.00	$75.00
7 purchase totals =	$841.98		$904.1367	$904.13	$904.10	$904.00