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	$23.59	5.181%	$24.8122	$24.81	$24.80	$24.80
Purchase #2	$59.66	4.185%	$62.1568	$62.16	$62.15	$62.20
Purchase #3	$217.91	13.342%	$246.9836	$246.98	$247.00	$247.00
Purchase #4	$26.99	4.206%	$28.1252	$28.13	$28.15	$28.10
Purchase #5	$154.27	12.671%	$173.8176	$173.82	$173.80	$173.80
Purchase #6	$217.79	4.436%	$227.4512	$227.45	$227.45	$227.50
Purchase #7	$67.59	5.206%	$71.1087	$71.11	$71.10	$71.10
7 purchase totals =	$767.80		$834.4553	$834.46	$834.45	$834.50