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	$237.61	4.318%	$247.87	$247.87	$247.85	$247.90
Purchase #2	$194.66	9.647%	$213.4389	$213.44	$213.45	$213.40
Purchase #3	$27.29	5.459%	$28.7798	$28.78	$28.80	$28.80
Purchase #4	$37.73	4.592%	$39.4626	$39.46	$39.45	$39.50
Purchase #5	$31.98	10.397%	$35.305	$35.31	$35.30	$35.30
Purchase #6	$74.62	5.390%	$78.642	$78.64	$78.65	$78.60
Purchase #7	$132.61	3.357%	$137.0617	$137.06	$137.05	$137.10
7 purchase totals =	$736.50		$780.5600	$780.56	$780.55	$780.60