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	$77.67	9.744%	$85.2382	$85.24	$85.25	$85.20
Purchase #2	$42.69	6.181%	$45.3287	$45.33	$45.35	$45.30
Purchase #3	$41.75	6.519%	$44.4717	$44.47	$44.45	$44.50
Purchase #4	$128.68	12.835%	$145.1961	$145.20	$145.20	$145.20
Purchase #5	$32.69	7.153%	$35.0283	$35.03	$35.05	$35.00
Purchase #6	$62.54	7.663%	$67.3324	$67.33	$67.35	$67.30
Purchase #7	$146.25	13.307%	$165.7115	$165.71	$165.70	$165.70
7 purchase totals =	$532.27		$588.3069	$588.31	$588.35	$588.20