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	$72.31	9.192%	$78.9567	$78.96	$78.95	$79.00
Purchase #2	$216.98	5.657%	$229.2546	$229.25	$229.25	$229.30
Purchase #3	$240.53	6.262%	$255.592	$255.59	$255.60	$255.60
Purchase #4	$70.49	3.322%	$72.8317	$72.83	$72.85	$72.80
Purchase #5	$133.87	10.491%	$147.9143	$147.91	$147.90	$147.90
Purchase #6	$23.57	10.509%	$26.047	$26.05	$26.05	$26.00
Purchase #7	$59.72	8.498%	$64.795	$64.80	$64.80	$64.80
7 purchase totals =	$817.47		$875.3913	$875.39	$875.40	$875.40