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	$250.32	3.113%	$258.1125	$258.11	$258.10	$258.10
Purchase #2	$241.76	3.536%	$250.3086	$250.31	$250.30	$250.30
Purchase #3	$77.95	5.231%	$82.0276	$82.03	$82.05	$82.00
Purchase #4	$120.59	6.454%	$128.3729	$128.37	$128.35	$128.40
Purchase #5	$29.44	7.247%	$31.5735	$31.57	$31.55	$31.60
Purchase #6	$30.31	12.348%	$34.0527	$34.05	$34.05	$34.10
Purchase #7	$207.99	12.836%	$234.6876	$234.69	$234.70	$234.70
7 purchase totals =	$958.36		$1,019.1354	$1,019.13	$1,019.10	$1,019.20