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	$35.50	8.623%	$38.5612	$38.56	$38.55	$38.60
Purchase #2	$118.66	7.450%	$127.5002	$127.50	$127.50	$127.50
Purchase #3	$148.57	3.832%	$154.2632	$154.26	$154.25	$154.30
Purchase #4	$64.68	9.854%	$71.0536	$71.05	$71.05	$71.10
Purchase #5	$22.79	11.784%	$25.4756	$25.48	$25.50	$25.50
Purchase #6	$35.59	13.242%	$40.3028	$40.30	$40.30	$40.30
Purchase #7	$164.90	8.517%	$178.9445	$178.94	$178.95	$178.90
7 purchase totals =	$590.69		$636.1011	$636.09	$636.10	$636.20