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	$119.99	5.792%	$126.9398	$126.94	$126.95	$126.90
Purchase #2	$241.30	11.826%	$269.8361	$269.84	$269.85	$269.80
Purchase #3	$206.68	10.786%	$228.9725	$228.97	$228.95	$229.00
Purchase #4	$17.51	7.531%	$18.8287	$18.83	$18.85	$18.80
Purchase #5	$85.31	5.591%	$90.0797	$90.08	$90.10	$90.10
Purchase #6	$222.69	9.196%	$243.1686	$243.17	$243.15	$243.20
Purchase #7	$33.31	7.205%	$35.71	$35.71	$35.70	$35.70
7 purchase totals =	$926.79		$1,013.5354	$1,013.54	$1,013.55	$1,013.50