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	$82.31	10.772%	$91.1764	$91.18	$91.20	$91.20
Purchase #2	$108.39	8.411%	$117.5067	$117.51	$117.50	$117.50
Purchase #3	$140.60	11.532%	$156.814	$156.81	$156.80	$156.80
Purchase #4	$53.47	7.664%	$57.5679	$57.57	$57.55	$57.60
Purchase #5	$93.84	11.323%	$104.4655	$104.47	$104.45	$104.50
Purchase #6	$22.67	10.842%	$25.1279	$25.13	$25.15	$25.10
Purchase #7	$224.33	8.841%	$244.163	$244.16	$244.15	$244.20
7 purchase totals =	$725.61		$796.8214	$796.83	$796.80	$796.90