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	$79.44	12.217%	$89.1452	$89.15	$89.15	$89.10
Purchase #2	$149.68	6.119%	$158.8389	$158.84	$158.85	$158.80
Purchase #3	$9.46	6.393%	$10.0648	$10.06	$10.05	$10.10
Purchase #4	$78.67	12.592%	$88.5761	$88.58	$88.60	$88.60
Purchase #5	$100.67	7.511%	$108.2313	$108.23	$108.25	$108.20
Purchase #6	$41.98	12.143%	$47.0776	$47.08	$47.10	$47.10
Purchase #7	$135.66	6.342%	$144.2636	$144.26	$144.25	$144.30
7 purchase totals =	$595.56		$646.1975	$646.20	$646.25	$646.20