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	$48.40	5.170%	$50.9023	$50.90	$50.90	$50.90
Purchase #2	$238.25	11.138%	$264.7863	$264.79	$264.80	$264.80
Purchase #3	$176.95	4.828%	$185.4931	$185.49	$185.50	$185.50
Purchase #4	$130.67	10.195%	$143.9918	$143.99	$144.00	$144.00
Purchase #5	$31.91	12.547%	$35.9137	$35.91	$35.90	$35.90
Purchase #6	$32.52	10.309%	$35.8725	$35.87	$35.85	$35.90
Purchase #7	$237.36	11.290%	$264.1579	$264.16	$264.15	$264.20
7 purchase totals =	$896.06		$981.1176	$981.11	$981.10	$981.20