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	$155.61	11.730%	$173.8631	$173.86	$173.85	$173.90
Purchase #2	$52.56	9.627%	$57.62	$57.62	$57.60	$57.60
Purchase #3	$122.90	12.818%	$138.6533	$138.65	$138.65	$138.70
Purchase #4	$76.60	7.383%	$82.2554	$82.26	$82.25	$82.30
Purchase #5	$83.29	4.341%	$86.9056	$86.91	$86.90	$86.90
Purchase #6	$71.36	6.708%	$76.1468	$76.15	$76.15	$76.10
Purchase #7	$77.78	6.563%	$82.8847	$82.88	$82.90	$82.90
7 purchase totals =	$640.10		$698.3289	$698.33	$698.30	$698.40