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	$30.50	9.148%	$33.2901	$33.29	$33.30	$33.30
Purchase #2	$149.94	4.422%	$156.5703	$156.57	$156.55	$156.60
Purchase #3	$63.67	11.404%	$70.9309	$70.93	$70.95	$70.90
Purchase #4	$99.62	3.674%	$103.28	$103.28	$103.30	$103.30
Purchase #5	$142.45	6.381%	$151.5397	$151.54	$151.55	$151.50
Purchase #6	$25.60	11.665%	$28.5862	$28.59	$28.60	$28.60
Purchase #7	$31.40	13.466%	$35.6283	$35.63	$35.65	$35.60
7 purchase totals =	$543.18		$579.8255	$579.83	$579.90	$579.80