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	$147.50	13.161%	$166.9125	$166.91	$166.90	$166.90
Purchase #2	$214.77	13.456%	$243.6695	$243.67	$243.65	$243.70
Purchase #3	$20.94	6.340%	$22.2676	$22.27	$22.25	$22.30
Purchase #4	$250.88	11.540%	$279.8316	$279.83	$279.85	$279.80
Purchase #5	$114.27	12.497%	$128.5503	$128.55	$128.55	$128.60
Purchase #6	$110.63	9.225%	$120.8356	$120.84	$120.85	$120.80
Purchase #7	$101.91	7.499%	$109.5522	$109.55	$109.55	$109.60
7 purchase totals =	$960.90		$1,071.6193	$1,071.62	$1,071.60	$1,071.70