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	$30.44	5.322%	$32.06	$32.06	$32.05	$32.10
Purchase #2	$42.55	9.540%	$46.6093	$46.61	$46.60	$46.60
Purchase #3	$107.86	4.391%	$112.5961	$112.60	$112.60	$112.60
Purchase #4	$55.56	8.737%	$60.4143	$60.41	$60.40	$60.40
Purchase #5	$211.46	12.607%	$238.1188	$238.12	$238.10	$238.10
Purchase #6	$27.28	4.611%	$28.5379	$28.54	$28.55	$28.50
Purchase #7	$137.67	4.558%	$143.945	$143.95	$143.95	$143.90
7 purchase totals =	$612.82		$662.2814	$662.29	$662.25	$662.20