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	$75.65	3.463%	$78.2698	$78.27	$78.25	$78.30
Purchase #2	$226.28	3.261%	$233.659	$233.66	$233.65	$233.70
Purchase #3	$103.78	12.591%	$116.8469	$116.85	$116.85	$116.80
Purchase #4	$118.84	8.864%	$129.374	$129.37	$129.35	$129.40
Purchase #5	$165.87	11.556%	$185.0379	$185.04	$185.05	$185.00
Purchase #6	$165.69	10.749%	$183.5	$183.50	$183.50	$183.50
Purchase #7	$234.56	13.128%	$265.353	$265.35	$265.35	$265.40
7 purchase totals =	$1,090.67		$1,192.0406	$1,192.04	$1,192.00	$1,192.10