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	$55.87	5.837%	$59.1311	$59.13	$59.15	$59.10
Purchase #2	$151.30	13.438%	$171.6317	$171.63	$171.65	$171.60
Purchase #3	$6.35	10.748%	$7.0325	$7.03	$7.05	$7.00
Purchase #4	$242.62	9.196%	$264.9313	$264.93	$264.95	$264.90
Purchase #5	$49.84	12.298%	$55.9693	$55.97	$55.95	$56.00
Purchase #6	$118.37	10.105%	$130.3313	$130.33	$130.35	$130.30
Purchase #7	$30.80	13.804%	$35.0516	$35.05	$35.05	$35.10
7 purchase totals =	$655.15		$724.0788	$724.07	$724.15	$724.00