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	$100.88	10.817%	$111.7922	$111.79	$111.80	$111.80
Purchase #2	$169.93	5.501%	$179.2778	$179.28	$179.30	$179.30
Purchase #3	$29.41	10.869%	$32.6066	$32.61	$32.60	$32.60
Purchase #4	$50.86	5.192%	$53.5007	$53.50	$53.50	$53.50
Purchase #5	$180.90	10.328%	$199.5834	$199.58	$199.60	$199.60
Purchase #6	$178.95	7.838%	$192.9761	$192.98	$193.00	$193.00
Purchase #7	$23.90	10.498%	$26.409	$26.41	$26.40	$26.40
7 purchase totals =	$734.83		$796.1458	$796.15	$796.20	$796.20