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	$199.90	8.268%	$216.4277	$216.43	$216.45	$216.40
Purchase #2	$91.28	13.543%	$103.6421	$103.64	$103.65	$103.60
Purchase #3	$161.51	6.233%	$171.5769	$171.58	$171.60	$171.60
Purchase #4	$17.89	13.847%	$20.3672	$20.37	$20.35	$20.40
Purchase #5	$65.79	7.171%	$70.5078	$70.51	$70.50	$70.50
Purchase #6	$116.54	11.799%	$130.2906	$130.29	$130.30	$130.30
Purchase #7	$72.41	6.420%	$77.0587	$77.06	$77.05	$77.10
7 purchase totals =	$725.32		$789.8710	$789.88	$789.90	$789.90