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	$30.81	4.847%	$32.3034	$32.30	$32.30	$32.30
Purchase #2	$90.70	10.172%	$99.926	$99.93	$99.95	$99.90
Purchase #3	$122.52	11.695%	$136.8487	$136.85	$136.85	$136.80
Purchase #4	$153.65	6.626%	$163.8308	$163.83	$163.85	$163.80
Purchase #5	$62.81	11.817%	$70.2323	$70.23	$70.25	$70.20
Purchase #6	$147.64	5.706%	$156.0643	$156.06	$156.05	$156.10
Purchase #7	$155.92	9.841%	$171.2641	$171.26	$171.25	$171.30
7 purchase totals =	$764.05		$830.4696	$830.46	$830.50	$830.40