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	$98.81	13.164%	$111.8173	$111.82	$111.80	$111.80
Purchase #2	$170.60	6.397%	$181.5133	$181.51	$181.50	$181.50
Purchase #3	$156.46	12.599%	$176.1724	$176.17	$176.15	$176.20
Purchase #4	$162.79	5.770%	$172.183	$172.18	$172.20	$172.20
Purchase #5	$250.30	11.498%	$279.0795	$279.08	$279.10	$279.10
Purchase #6	$11.89	11.590%	$13.2681	$13.27	$13.25	$13.30
Purchase #7	$91.66	7.666%	$98.6867	$98.69	$98.70	$98.70
7 purchase totals =	$942.51		$1,032.7203	$1,032.72	$1,032.70	$1,032.80