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	$201.96	13.674%	$229.576	$229.58	$229.60	$229.60
Purchase #2	$164.35	3.413%	$169.9593	$169.96	$169.95	$170.00
Purchase #3	$46.36	10.738%	$51.3381	$51.34	$51.35	$51.30
Purchase #4	$36.89	10.721%	$40.845	$40.85	$40.85	$40.80
Purchase #5	$93.34	10.500%	$103.1407	$103.14	$103.15	$103.10
Purchase #6	$179.76	6.677%	$191.7626	$191.76	$191.75	$191.80
Purchase #7	$139.86	3.768%	$145.1299	$145.13	$145.15	$145.10
7 purchase totals =	$862.52		$931.7516	$931.76	$931.80	$931.70