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	$161.78	12.166%	$181.4622	$181.46	$181.45	$181.50
Purchase #2	$250.26	10.616%	$276.8276	$276.83	$276.85	$276.80
Purchase #3	$15.88	13.661%	$18.0494	$18.05	$18.05	$18.00
Purchase #4	$55.34	7.622%	$59.558	$59.56	$59.55	$59.60
Purchase #5	$114.71	7.170%	$122.9347	$122.93	$122.95	$122.90
Purchase #6	$247.89	13.816%	$282.1385	$282.14	$282.15	$282.10
Purchase #7	$205.49	4.701%	$215.1501	$215.15	$215.15	$215.20
7 purchase totals =	$1,051.35		$1,156.1205	$1,156.12	$1,156.15	$1,156.10