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	$108.73	10.281%	$119.9085	$119.91	$119.90	$119.90
Purchase #2	$48.44	13.172%	$54.8205	$54.82	$54.80	$54.80
Purchase #3	$171.55	6.261%	$182.2907	$182.29	$182.30	$182.30
Purchase #4	$220.82	3.641%	$228.8601	$228.86	$228.85	$228.90
Purchase #5	$151.27	3.214%	$156.1318	$156.13	$156.15	$156.10
Purchase #6	$42.42	7.542%	$45.6193	$45.62	$45.60	$45.60
Purchase #7	$16.61	8.435%	$18.0111	$18.01	$18.00	$18.00
7 purchase totals =	$759.84		$805.6420	$805.64	$805.60	$805.60