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	$242.29	6.715%	$258.5598	$258.56	$258.55	$258.60
Purchase #2	$90.59	7.464%	$97.3516	$97.35	$97.35	$97.40
Purchase #3	$127.69	12.391%	$143.5121	$143.51	$143.50	$143.50
Purchase #4	$12.70	4.115%	$13.2226	$13.22	$13.20	$13.20
Purchase #5	$6.74	11.138%	$7.4907	$7.49	$7.50	$7.50
Purchase #6	$124.36	13.426%	$141.0566	$141.06	$141.05	$141.10
Purchase #7	$191.52	3.440%	$198.1083	$198.11	$198.10	$198.10
7 purchase totals =	$795.89		$859.3017	$859.30	$859.25	$859.40