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	$74.44	11.120%	$82.7177	$82.72	$82.70	$82.70
Purchase #2	$203.90	5.304%	$214.7149	$214.71	$214.70	$214.70
Purchase #3	$175.43	5.650%	$185.3418	$185.34	$185.35	$185.30
Purchase #4	$172.42	4.687%	$180.5013	$180.50	$180.50	$180.50
Purchase #5	$165.86	8.202%	$179.4638	$179.46	$179.45	$179.50
Purchase #6	$132.45	7.681%	$142.6235	$142.62	$142.60	$142.60
Purchase #7	$159.75	5.163%	$167.9979	$168.00	$168.00	$168.00
7 purchase totals =	$1,084.25		$1,153.3609	$1,153.35	$1,153.30	$1,153.30