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	$172.79	8.682%	$187.7916	$187.79	$187.80	$187.80
Purchase #2	$87.81	13.304%	$99.4922	$99.49	$99.50	$99.50
Purchase #3	$198.87	3.261%	$205.3552	$205.36	$205.35	$205.40
Purchase #4	$217.80	9.515%	$238.5237	$238.52	$238.50	$238.50
Purchase #5	$80.69	13.826%	$91.8462	$91.85	$91.85	$91.80
Purchase #6	$180.29	6.809%	$192.5659	$192.57	$192.55	$192.60
Purchase #7	$48.98	3.162%	$50.5287	$50.53	$50.55	$50.50
7 purchase totals =	$987.23		$1,066.1035	$1,066.11	$1,066.10	$1,066.10