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	$155.61	11.755%	$173.902	$173.90	$173.90	$173.90
Purchase #2	$230.28	4.333%	$240.258	$240.26	$240.25	$240.30
Purchase #3	$33.78	5.346%	$35.5859	$35.59	$35.60	$35.60
Purchase #4	$106.29	3.540%	$110.0527	$110.05	$110.05	$110.10
Purchase #5	$77.54	10.114%	$85.3824	$85.38	$85.40	$85.40
Purchase #6	$41.48	9.523%	$45.4301	$45.43	$45.45	$45.40
Purchase #7	$68.68	7.154%	$73.5934	$73.59	$73.60	$73.60
7 purchase totals =	$713.66		$764.2045	$764.20	$764.25	$764.30