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	$30.90	7.537%	$33.2289	$33.23	$33.25	$33.20
Purchase #2	$64.68	11.723%	$72.2624	$72.26	$72.25	$72.30
Purchase #3	$197.62	11.342%	$220.0341	$220.03	$220.05	$220.00
Purchase #4	$238.58	4.829%	$250.101	$250.10	$250.10	$250.10
Purchase #5	$73.45	6.704%	$78.3741	$78.37	$78.35	$78.40
Purchase #6	$111.83	5.810%	$118.3273	$118.33	$118.35	$118.30
Purchase #7	$128.51	13.499%	$145.8576	$145.86	$145.85	$145.90
7 purchase totals =	$845.57		$918.1854	$918.18	$918.20	$918.20