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	$154.41	7.111%	$165.3901	$165.39	$165.40	$165.40
Purchase #2	$115.46	11.155%	$128.3396	$128.34	$128.35	$128.30
Purchase #3	$181.56	6.361%	$193.109	$193.11	$193.10	$193.10
Purchase #4	$81.59	10.770%	$90.3772	$90.38	$90.40	$90.40
Purchase #5	$141.39	8.533%	$153.4548	$153.45	$153.45	$153.50
Purchase #6	$9.56	10.574%	$10.5709	$10.57	$10.55	$10.60
Purchase #7	$138.56	12.172%	$155.4255	$155.43	$155.45	$155.40
7 purchase totals =	$822.53		$896.6671	$896.67	$896.70	$896.70