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	$114.71	13.756%	$130.4895	$130.49	$130.50	$130.50
Purchase #2	$33.60	11.388%	$37.4264	$37.43	$37.45	$37.40
Purchase #3	$191.33	4.736%	$200.3914	$200.39	$200.40	$200.40
Purchase #4	$72.41	5.381%	$76.3064	$76.31	$76.30	$76.30
Purchase #5	$178.92	9.613%	$196.1196	$196.12	$196.10	$196.10
Purchase #6	$153.34	7.667%	$165.0966	$165.10	$165.10	$165.10
Purchase #7	$43.48	4.224%	$45.3166	$45.32	$45.30	$45.30
7 purchase totals =	$787.79		$851.1465	$851.16	$851.15	$851.10