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	$18.42	9.842%	$20.2329	$20.23	$20.25	$20.20
Purchase #2	$120.96	5.862%	$128.0507	$128.05	$128.05	$128.10
Purchase #3	$34.30	7.525%	$36.8811	$36.88	$36.90	$36.90
Purchase #4	$171.72	11.195%	$190.9441	$190.94	$190.95	$190.90
Purchase #5	$80.95	10.106%	$89.1308	$89.13	$89.15	$89.10
Purchase #6	$129.47	6.232%	$137.5386	$137.54	$137.55	$137.50
Purchase #7	$67.74	5.829%	$71.6886	$71.69	$71.70	$71.70
7 purchase totals =	$623.56		$674.4668	$674.46	$674.55	$674.40