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	$81.74	9.468%	$89.4791	$89.48	$89.50	$89.50
Purchase #2	$55.51	12.658%	$62.5365	$62.54	$62.55	$62.50
Purchase #3	$195.30	7.848%	$210.6271	$210.63	$210.65	$210.60
Purchase #4	$170.33	7.668%	$183.3909	$183.39	$183.40	$183.40
Purchase #5	$128.41	7.567%	$138.1268	$138.13	$138.15	$138.10
Purchase #6	$125.77	3.368%	$130.0059	$130.01	$130.00	$130.00
Purchase #7	$56.76	8.150%	$61.3859	$61.39	$61.40	$61.40
7 purchase totals =	$813.82		$875.5522	$875.57	$875.65	$875.50