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	$92.70	6.680%	$98.8924	$98.89	$98.90	$98.90
Purchase #2	$56.54	12.345%	$63.5199	$63.52	$63.50	$63.50
Purchase #3	$83.26	8.634%	$90.4487	$90.45	$90.45	$90.40
Purchase #4	$31.67	13.854%	$36.0576	$36.06	$36.05	$36.10
Purchase #5	$70.30	5.779%	$74.3626	$74.36	$74.35	$74.40
Purchase #6	$168.90	6.311%	$179.5593	$179.56	$179.55	$179.60
Purchase #7	$208.66	4.217%	$217.4592	$217.46	$217.45	$217.50
7 purchase totals =	$712.03		$760.2997	$760.30	$760.25	$760.40