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	$67.83	13.702%	$77.1241	$77.12	$77.10	$77.10
Purchase #2	$123.88	6.320%	$131.7092	$131.71	$131.70	$131.70
Purchase #3	$154.40	13.809%	$175.7211	$175.72	$175.70	$175.70
Purchase #4	$158.37	8.718%	$172.1767	$172.18	$172.20	$172.20
Purchase #5	$97.60	6.725%	$104.1636	$104.16	$104.15	$104.20
Purchase #6	$101.88	8.780%	$110.8251	$110.83	$110.85	$110.80
Purchase #7	$238.37	7.320%	$255.8187	$255.82	$255.80	$255.80
7 purchase totals =	$942.33		$1,027.5385	$1,027.54	$1,027.50	$1,027.50