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	$165.27	3.524%	$171.0941	$171.09	$171.10	$171.10
Purchase #2	$82.77	8.213%	$89.5679	$89.57	$89.55	$89.60
Purchase #3	$129.61	9.289%	$141.6495	$141.65	$141.65	$141.60
Purchase #4	$41.50	5.336%	$43.7144	$43.71	$43.70	$43.70
Purchase #5	$16.97	9.274%	$18.5438	$18.54	$18.55	$18.50
Purchase #6	$130.78	5.214%	$137.5989	$137.60	$137.60	$137.60
Purchase #7	$23.59	5.240%	$24.8261	$24.83	$24.85	$24.80
7 purchase totals =	$590.49		$626.9947	$626.99	$627.00	$626.90