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	$79.50	13.637%	$90.3414	$90.34	$90.35	$90.30
Purchase #2	$245.84	9.198%	$268.4524	$268.45	$268.45	$268.50
Purchase #3	$169.50	8.545%	$183.9838	$183.98	$184.00	$184.00
Purchase #4	$132.45	7.664%	$142.601	$142.60	$142.60	$142.60
Purchase #5	$235.72	10.728%	$261.008	$261.01	$261.00	$261.00
Purchase #6	$46.82	4.216%	$48.7939	$48.79	$48.80	$48.80
Purchase #7	$146.29	3.574%	$151.5184	$151.52	$151.50	$151.50
7 purchase totals =	$1,056.12		$1,146.6989	$1,146.69	$1,146.70	$1,146.70