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	$88.33	13.287%	$100.0664	$100.07	$100.05	$100.10
Purchase #2	$225.40	12.599%	$253.7981	$253.80	$253.80	$253.80
Purchase #3	$211.48	12.693%	$238.3232	$238.32	$238.30	$238.30
Purchase #4	$142.65	10.444%	$157.5484	$157.55	$157.55	$157.50
Purchase #5	$80.49	3.471%	$83.2838	$83.28	$83.30	$83.30
Purchase #6	$190.90	9.740%	$209.4937	$209.49	$209.50	$209.50
Purchase #7	$139.81	8.407%	$151.5638	$151.56	$151.55	$151.60
7 purchase totals =	$1,079.06		$1,194.0774	$1,194.07	$1,194.05	$1,194.10