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	$27.92	7.118%	$29.9073	$29.91	$29.90	$29.90
Purchase #2	$45.98	12.850%	$51.8884	$51.89	$51.90	$51.90
Purchase #3	$62.58	11.707%	$69.9062	$69.91	$69.90	$69.90
Purchase #4	$99.94	13.674%	$113.6058	$113.61	$113.60	$113.60
Purchase #5	$73.46	9.354%	$80.3314	$80.33	$80.35	$80.30
Purchase #6	$42.89	5.613%	$45.2974	$45.30	$45.30	$45.30
Purchase #7	$60.51	6.542%	$64.4686	$64.47	$64.45	$64.50
7 purchase totals =	$413.28		$455.4051	$455.42	$455.40	$455.40