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	$116.32	9.454%	$127.3169	$127.32	$127.30	$127.30
Purchase #2	$226.95	9.398%	$248.2788	$248.28	$248.30	$248.30
Purchase #3	$114.56	7.429%	$123.0707	$123.07	$123.05	$123.10
Purchase #4	$45.88	5.683%	$48.4874	$48.49	$48.50	$48.50
Purchase #5	$165.26	10.678%	$182.9065	$182.91	$182.90	$182.90
Purchase #6	$7.88	5.461%	$8.3103	$8.31	$8.30	$8.30
Purchase #7	$83.33	9.477%	$91.2272	$91.23	$91.25	$91.20
7 purchase totals =	$760.18		$829.5978	$829.61	$829.60	$829.60