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	$187.46	6.268%	$199.21	$199.21	$199.20	$199.20
Purchase #2	$103.99	7.529%	$111.8194	$111.82	$111.80	$111.80
Purchase #3	$44.48	4.287%	$46.3869	$46.39	$46.40	$46.40
Purchase #4	$210.46	13.709%	$239.312	$239.31	$239.30	$239.30
Purchase #5	$246.41	3.852%	$255.9017	$255.90	$255.90	$255.90
Purchase #6	$191.25	12.644%	$215.4317	$215.43	$215.45	$215.40
Purchase #7	$41.66	8.275%	$45.1074	$45.11	$45.10	$45.10
7 purchase totals =	$1,025.71		$1,113.1691	$1,113.17	$1,113.15	$1,113.10