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	$39.43	9.131%	$43.0304	$43.03	$43.05	$43.00
Purchase #2	$154.62	4.531%	$161.6258	$161.63	$161.65	$161.60
Purchase #3	$45.25	9.399%	$49.503	$49.50	$49.50	$49.50
Purchase #4	$108.55	6.228%	$115.3105	$115.31	$115.30	$115.30
Purchase #5	$86.31	4.167%	$89.9065	$89.91	$89.90	$89.90
Purchase #6	$100.71	10.843%	$111.63	$111.63	$111.65	$111.60
Purchase #7	$233.77	9.845%	$256.7847	$256.78	$256.80	$256.80
7 purchase totals =	$768.64		$827.7909	$827.79	$827.85	$827.70