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	$64.87	8.643%	$70.4767	$70.48	$70.50	$70.50
Purchase #2	$134.57	6.242%	$142.9699	$142.97	$142.95	$143.00
Purchase #3	$18.97	12.105%	$21.2663	$21.27	$21.25	$21.30
Purchase #4	$110.96	6.288%	$117.9372	$117.94	$117.95	$117.90
Purchase #5	$244.37	8.367%	$264.8164	$264.82	$264.80	$264.80
Purchase #6	$66.60	8.296%	$72.1251	$72.13	$72.15	$72.10
Purchase #7	$101.49	10.652%	$112.3007	$112.30	$112.30	$112.30
7 purchase totals =	$741.83		$801.8923	$801.91	$801.90	$801.90