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	$130.69	6.802%	$139.5795	$139.58	$139.60	$139.60
Purchase #2	$30.30	8.422%	$32.8519	$32.85	$32.85	$32.90
Purchase #3	$106.32	8.716%	$115.5869	$115.59	$115.60	$115.60
Purchase #4	$163.30	13.794%	$185.8256	$185.83	$185.85	$185.80
Purchase #5	$153.46	11.377%	$170.9191	$170.92	$170.90	$170.90
Purchase #6	$96.52	6.862%	$103.1432	$103.14	$103.15	$103.10
Purchase #7	$140.63	10.309%	$155.1275	$155.13	$155.15	$155.10
7 purchase totals =	$821.22		$903.0337	$903.04	$903.10	$903.00