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	$123.90	4.494%	$129.4681	$129.47	$129.45	$129.50
Purchase #2	$85.57	7.720%	$92.176	$92.18	$92.20	$92.20
Purchase #3	$221.80	12.370%	$249.2367	$249.24	$249.25	$249.20
Purchase #4	$114.49	7.577%	$123.1649	$123.16	$123.15	$123.20
Purchase #5	$57.40	13.357%	$65.0669	$65.07	$65.05	$65.10
Purchase #6	$10.47	13.173%	$11.8492	$11.85	$11.85	$11.80
Purchase #7	$148.39	3.708%	$153.8923	$153.89	$153.90	$153.90
7 purchase totals =	$762.02		$824.8541	$824.86	$824.85	$824.90