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	$41.46	4.111%	$43.1644	$43.16	$43.15	$43.20
Purchase #2	$20.29	12.441%	$22.8143	$22.81	$22.80	$22.80
Purchase #3	$128.73	12.795%	$145.201	$145.20	$145.20	$145.20
Purchase #4	$232.35	13.852%	$264.5351	$264.54	$264.55	$264.50
Purchase #5	$65.64	6.323%	$69.7904	$69.79	$69.80	$69.80
Purchase #6	$76.29	3.428%	$78.9052	$78.91	$78.90	$78.90
Purchase #7	$57.67	3.540%	$59.7115	$59.71	$59.70	$59.70
7 purchase totals =	$622.43		$684.1219	$684.12	$684.10	$684.10