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	$156.61	7.517%	$168.3824	$168.38	$168.40	$168.40
Purchase #2	$100.30	10.265%	$110.5958	$110.60	$110.60	$110.60
Purchase #3	$234.38	11.694%	$261.7884	$261.79	$261.80	$261.80
Purchase #4	$59.94	10.233%	$66.0737	$66.07	$66.05	$66.10
Purchase #5	$145.61	4.480%	$152.1333	$152.13	$152.15	$152.10
Purchase #6	$88.88	8.257%	$96.2188	$96.22	$96.20	$96.20
Purchase #7	$239.64	4.575%	$250.6035	$250.60	$250.60	$250.60
7 purchase totals =	$1,025.36		$1,105.7959	$1,105.79	$1,105.80	$1,105.80