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	$91.84	13.383%	$104.1309	$104.13	$104.15	$104.10
Purchase #2	$129.32	9.349%	$141.4101	$141.41	$141.40	$141.40
Purchase #3	$18.59	4.570%	$19.4396	$19.44	$19.45	$19.40
Purchase #4	$18.83	10.238%	$20.7578	$20.76	$20.75	$20.80
Purchase #5	$93.84	10.709%	$103.8893	$103.89	$103.90	$103.90
Purchase #6	$206.29	5.739%	$218.129	$218.13	$218.15	$218.10
Purchase #7	$11.31	12.472%	$12.7206	$12.72	$12.70	$12.70
7 purchase totals =	$570.02		$620.4773	$620.48	$620.50	$620.40