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	$247.34	12.581%	$278.4578	$278.46	$278.45	$278.50
Purchase #2	$52.83	13.221%	$59.8147	$59.81	$59.80	$59.80
Purchase #3	$49.82	6.696%	$53.1559	$53.16	$53.15	$53.20
Purchase #4	$103.92	3.244%	$107.2912	$107.29	$107.30	$107.30
Purchase #5	$188.39	4.115%	$196.1422	$196.14	$196.15	$196.10
Purchase #6	$5.31	9.183%	$5.7976	$5.80	$5.80	$5.80
Purchase #7	$209.35	7.514%	$225.0806	$225.08	$225.10	$225.10
7 purchase totals =	$856.96		$925.7400	$925.74	$925.75	$925.80