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	$33.70	6.269%	$35.8127	$35.81	$35.80	$35.80
Purchase #2	$56.38	4.839%	$59.1082	$59.11	$59.10	$59.10
Purchase #3	$69.41	11.186%	$77.1742	$77.17	$77.15	$77.20
Purchase #4	$165.36	8.752%	$179.8323	$179.83	$179.85	$179.80
Purchase #5	$112.84	13.223%	$127.7608	$127.76	$127.75	$127.80
Purchase #6	$233.84	11.471%	$260.6638	$260.66	$260.65	$260.70
Purchase #7	$166.45	8.750%	$181.0144	$181.01	$181.00	$181.00
7 purchase totals =	$837.98		$921.3664	$921.35	$921.30	$921.40