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	$98.41	6.114%	$104.4268	$104.43	$104.45	$104.40
Purchase #2	$151.29	11.320%	$168.416	$168.42	$168.40	$168.40
Purchase #3	$132.70	13.775%	$150.9794	$150.98	$151.00	$151.00
Purchase #4	$24.66	11.867%	$27.5864	$27.59	$27.60	$27.60
Purchase #5	$208.44	10.118%	$229.53	$229.53	$229.55	$229.50
Purchase #6	$85.74	4.845%	$89.8941	$89.89	$89.90	$89.90
Purchase #7	$175.95	7.182%	$188.5867	$188.59	$188.60	$188.60
7 purchase totals =	$877.19		$959.4194	$959.43	$959.50	$959.40