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	$151.42	3.705%	$157.0301	$157.03	$157.05	$157.00
Purchase #2	$91.35	9.201%	$99.7551	$99.76	$99.75	$99.80
Purchase #3	$36.71	4.109%	$38.2184	$38.22	$38.20	$38.20
Purchase #4	$232.62	8.282%	$251.8856	$251.89	$251.90	$251.90
Purchase #5	$112.96	9.161%	$123.3083	$123.31	$123.30	$123.30
Purchase #6	$14.28	7.150%	$15.301	$15.30	$15.30	$15.30
Purchase #7	$191.91	4.359%	$200.2754	$200.28	$200.30	$200.30
7 purchase totals =	$831.25		$885.7739	$885.79	$885.80	$885.80