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	$221.29	8.640%	$240.4095	$240.41	$240.40	$240.40
Purchase #2	$5.92	9.446%	$6.4792	$6.48	$6.50	$6.50
Purchase #3	$61.62	6.454%	$65.597	$65.60	$65.60	$65.60
Purchase #4	$138.44	4.240%	$144.3099	$144.31	$144.30	$144.30
Purchase #5	$89.75	10.585%	$99.25	$99.25	$99.25	$99.30
Purchase #6	$63.85	13.404%	$72.4085	$72.41	$72.40	$72.40
Purchase #7	$250.91	13.602%	$285.0388	$285.04	$285.05	$285.00
7 purchase totals =	$831.78		$913.4929	$913.50	$913.50	$913.50