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	$231.45	9.795%	$254.1205	$254.12	$254.10	$254.10
Purchase #2	$134.26	12.646%	$151.2385	$151.24	$151.25	$151.20
Purchase #3	$13.79	10.817%	$15.2817	$15.28	$15.30	$15.30
Purchase #4	$82.87	3.627%	$85.8757	$85.88	$85.90	$85.90
Purchase #5	$159.41	7.290%	$171.031	$171.03	$171.05	$171.00
Purchase #6	$190.65	9.863%	$209.4538	$209.45	$209.45	$209.50
Purchase #7	$52.47	4.533%	$54.8485	$54.85	$54.85	$54.80
7 purchase totals =	$864.90		$941.8497	$941.85	$941.90	$941.80