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	$93.43	10.243%	$103	$103.00	$103.00	$103.00
Purchase #2	$181.43	3.368%	$187.5406	$187.54	$187.55	$187.50
Purchase #3	$51.88	6.540%	$55.273	$55.27	$55.25	$55.30
Purchase #4	$9.68	4.490%	$10.1146	$10.11	$10.10	$10.10
Purchase #5	$144.38	12.657%	$162.6542	$162.65	$162.65	$162.70
Purchase #6	$65.84	11.218%	$73.2259	$73.23	$73.25	$73.20
Purchase #7	$27.83	13.154%	$31.4908	$31.49	$31.50	$31.50
7 purchase totals =	$574.47		$623.2991	$623.29	$623.30	$623.30