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	$109.72	9.709%	$120.3727	$120.37	$120.35	$120.40
Purchase #2	$70.70	10.402%	$78.0542	$78.05	$78.05	$78.10
Purchase #3	$28.91	12.661%	$32.5703	$32.57	$32.55	$32.60
Purchase #4	$38.81	10.317%	$42.814	$42.81	$42.80	$42.80
Purchase #5	$173.39	8.788%	$188.6275	$188.63	$188.65	$188.60
Purchase #6	$132.56	13.261%	$150.1388	$150.14	$150.15	$150.10
Purchase #7	$131.50	5.381%	$138.576	$138.58	$138.60	$138.60
7 purchase totals =	$685.59		$751.1535	$751.15	$751.15	$751.20