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	$151.73	9.158%	$165.6254	$165.63	$165.65	$165.60
Purchase #2	$226.43	9.711%	$248.4186	$248.42	$248.40	$248.40
Purchase #3	$61.76	4.473%	$64.5225	$64.52	$64.50	$64.50
Purchase #4	$232.83	10.864%	$258.1247	$258.12	$258.10	$258.10
Purchase #5	$11.98	12.254%	$13.448	$13.45	$13.45	$13.40
Purchase #6	$86.62	3.290%	$89.4698	$89.47	$89.45	$89.50
Purchase #7	$129.86	8.849%	$141.3513	$141.35	$141.35	$141.40
7 purchase totals =	$901.21		$980.9603	$980.96	$980.90	$980.90