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	$16.33	11.577%	$18.2205	$18.22	$18.20	$18.20
Purchase #2	$63.69	10.314%	$70.259	$70.26	$70.25	$70.30
Purchase #3	$19.27	12.475%	$21.6739	$21.67	$21.65	$21.70
Purchase #4	$74.57	5.566%	$78.7206	$78.72	$78.70	$78.70
Purchase #5	$165.80	8.678%	$180.1881	$180.19	$180.20	$180.20
Purchase #6	$145.84	5.258%	$153.5083	$153.51	$153.50	$153.50
Purchase #7	$81.61	4.510%	$85.2906	$85.29	$85.30	$85.30
7 purchase totals =	$567.11		$607.8610	$607.86	$607.80	$607.90