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	$35.89	11.486%	$40.0123	$40.01	$40.00	$40.00
Purchase #2	$223.46	6.107%	$237.1067	$237.11	$237.10	$237.10
Purchase #3	$13.87	9.267%	$15.1553	$15.16	$15.15	$15.20
Purchase #4	$66.72	6.599%	$71.1229	$71.12	$71.10	$71.10
Purchase #5	$242.25	7.520%	$260.4672	$260.47	$260.45	$260.50
Purchase #6	$109.31	11.728%	$122.1299	$122.13	$122.15	$122.10
Purchase #7	$234.95	13.594%	$266.8891	$266.89	$266.90	$266.90
7 purchase totals =	$926.45		$1,012.8834	$1,012.89	$1,012.85	$1,012.90