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	$27.29	5.849%	$28.8862	$28.89	$28.90	$28.90
Purchase #2	$114.32	13.787%	$130.0813	$130.08	$130.10	$130.10
Purchase #3	$226.96	8.268%	$245.7251	$245.73	$245.75	$245.70
Purchase #4	$247.46	12.848%	$279.2537	$279.25	$279.25	$279.30
Purchase #5	$141.45	6.434%	$150.5509	$150.55	$150.55	$150.60
Purchase #6	$173.94	3.156%	$179.4295	$179.43	$179.45	$179.40
Purchase #7	$240.75	9.395%	$263.3685	$263.37	$263.35	$263.40
7 purchase totals =	$1,172.17		$1,277.2952	$1,277.30	$1,277.35	$1,277.40