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	$73.34	9.147%	$80.0484	$80.05	$80.05	$80.00
Purchase #2	$67.89	5.271%	$71.4685	$71.47	$71.45	$71.50
Purchase #3	$214.43	10.665%	$237.299	$237.30	$237.30	$237.30
Purchase #4	$96.92	3.444%	$100.2579	$100.26	$100.25	$100.30
Purchase #5	$145.45	13.652%	$165.3068	$165.31	$165.30	$165.30
Purchase #6	$219.83	12.106%	$246.4426	$246.44	$246.45	$246.40
Purchase #7	$219.65	4.797%	$230.1866	$230.19	$230.20	$230.20
7 purchase totals =	$1,037.51		$1,131.0098	$1,131.02	$1,131.00	$1,131.00