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	$73.87	13.423%	$83.7856	$83.79	$83.80	$83.80
Purchase #2	$99.84	3.449%	$103.2835	$103.28	$103.30	$103.30
Purchase #3	$174.70	5.472%	$184.2596	$184.26	$184.25	$184.30
Purchase #4	$10.57	10.345%	$11.6635	$11.66	$11.65	$11.70
Purchase #5	$208.40	9.320%	$227.8229	$227.82	$227.80	$227.80
Purchase #6	$196.92	6.449%	$209.6194	$209.62	$209.60	$209.60
Purchase #7	$90.54	9.817%	$99.4283	$99.43	$99.45	$99.40
7 purchase totals =	$854.84		$919.8628	$919.86	$919.85	$919.90