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	$170.38	11.408%	$189.817	$189.82	$189.80	$189.80
Purchase #2	$19.42	4.556%	$20.3048	$20.30	$20.30	$20.30
Purchase #3	$83.87	9.590%	$91.9131	$91.91	$91.90	$91.90
Purchase #4	$34.79	13.451%	$39.4696	$39.47	$39.45	$39.50
Purchase #5	$169.87	7.461%	$182.544	$182.54	$182.55	$182.50
Purchase #6	$19.92	5.123%	$20.9405	$20.94	$20.95	$20.90
Purchase #7	$35.36	3.240%	$36.5057	$36.51	$36.50	$36.50
7 purchase totals =	$533.61		$581.4947	$581.49	$581.45	$581.40