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	$19.29	11.388%	$21.4867	$21.49	$21.50	$21.50
Purchase #2	$88.84	7.719%	$95.6976	$95.70	$95.70	$95.70
Purchase #3	$127.75	10.566%	$141.2481	$141.25	$141.25	$141.20
Purchase #4	$140.78	7.588%	$151.4624	$151.46	$151.45	$151.50
Purchase #5	$110.62	4.368%	$115.4519	$115.45	$115.45	$115.50
Purchase #6	$136.67	8.300%	$148.0136	$148.01	$148.00	$148.00
Purchase #7	$155.35	11.224%	$172.7865	$172.79	$172.80	$172.80
7 purchase totals =	$779.30		$846.1468	$846.15	$846.15	$846.20