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	$152.41	13.678%	$173.2566	$173.26	$173.25	$173.30
Purchase #2	$106.83	11.874%	$119.515	$119.52	$119.50	$119.50
Purchase #3	$146.91	10.649%	$162.5544	$162.55	$162.55	$162.60
Purchase #4	$92.93	8.458%	$100.79	$100.79	$100.80	$100.80
Purchase #5	$239.47	13.494%	$271.7841	$271.78	$271.80	$271.80
Purchase #6	$113.62	9.348%	$124.2412	$124.24	$124.25	$124.20
Purchase #7	$61.63	6.754%	$65.7925	$65.79	$65.80	$65.80
7 purchase totals =	$913.80		$1,017.9338	$1,017.93	$1,017.95	$1,018.00