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	$198.31	8.836%	$215.8327	$215.83	$215.85	$215.80
Purchase #2	$250.64	11.611%	$279.7418	$279.74	$279.75	$279.70
Purchase #3	$233.78	12.721%	$263.5192	$263.52	$263.50	$263.50
Purchase #4	$20.76	7.704%	$22.3594	$22.36	$22.35	$22.40
Purchase #5	$153.96	7.499%	$165.5055	$165.51	$165.50	$165.50
Purchase #6	$145.93	13.437%	$165.5386	$165.54	$165.55	$165.50
Purchase #7	$134.35	12.162%	$150.6896	$150.69	$150.70	$150.70
7 purchase totals =	$1,137.73		$1,263.1868	$1,263.19	$1,263.20	$1,263.10