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	$40.72	12.826%	$45.9427	$45.94	$45.95	$45.90
Purchase #2	$73.29	9.363%	$80.1521	$80.15	$80.15	$80.20
Purchase #3	$17.89	9.432%	$19.5774	$19.58	$19.60	$19.60
Purchase #4	$71.76	7.448%	$77.1047	$77.10	$77.10	$77.10
Purchase #5	$16.34	10.375%	$18.0353	$18.04	$18.05	$18.00
Purchase #6	$179.66	11.832%	$200.9174	$200.92	$200.90	$200.90
Purchase #7	$141.64	11.769%	$158.3096	$158.31	$158.30	$158.30
7 purchase totals =	$541.30		$600.0392	$600.04	$600.05	$600.00