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	$109.30	9.368%	$119.5392	$119.54	$119.55	$119.50
Purchase #2	$176.52	4.306%	$184.121	$184.12	$184.10	$184.10
Purchase #3	$202.43	4.622%	$211.7863	$211.79	$211.80	$211.80
Purchase #4	$109.46	12.869%	$123.5464	$123.55	$123.55	$123.50
Purchase #5	$42.69	12.743%	$48.13	$48.13	$48.15	$48.10
Purchase #6	$45.33	11.245%	$50.4274	$50.43	$50.45	$50.40
Purchase #7	$18.82	7.521%	$20.2355	$20.24	$20.25	$20.20
7 purchase totals =	$704.55		$757.7858	$757.80	$757.85	$757.60