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	$73.35	8.655%	$79.6984	$79.70	$79.70	$79.70
Purchase #2	$138.52	13.778%	$157.6053	$157.61	$157.60	$157.60
Purchase #3	$90.52	11.513%	$100.9416	$100.94	$100.95	$100.90
Purchase #4	$151.25	11.355%	$168.4244	$168.42	$168.40	$168.40
Purchase #5	$93.95	5.761%	$99.3625	$99.36	$99.35	$99.40
Purchase #6	$81.82	4.269%	$85.3129	$85.31	$85.30	$85.30
Purchase #7	$113.60	12.504%	$127.8045	$127.80	$127.80	$127.80
7 purchase totals =	$743.01		$819.1496	$819.14	$819.10	$819.10