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	$73.98	7.172%	$79.2858	$79.29	$79.30	$79.30
Purchase #2	$74.26	6.306%	$78.9428	$78.94	$78.95	$78.90
Purchase #3	$203.60	9.331%	$222.5979	$222.60	$222.60	$222.60
Purchase #4	$12.27	7.131%	$13.145	$13.15	$13.15	$13.10
Purchase #5	$141.68	11.546%	$158.0384	$158.04	$158.05	$158.00
Purchase #6	$121.52	8.285%	$131.5879	$131.59	$131.60	$131.60
Purchase #7	$166.98	8.823%	$181.7126	$181.71	$181.70	$181.70
7 purchase totals =	$794.29		$865.3104	$865.32	$865.35	$865.20