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	$50.59	6.342%	$53.7984	$53.80	$53.80	$53.80
Purchase #2	$99.73	4.691%	$104.4083	$104.41	$104.40	$104.40
Purchase #3	$100.33	5.587%	$105.9354	$105.94	$105.95	$105.90
Purchase #4	$79.52	7.848%	$85.7607	$85.76	$85.75	$85.80
Purchase #5	$33.27	12.340%	$37.3755	$37.38	$37.40	$37.40
Purchase #6	$122.34	6.240%	$129.974	$129.97	$129.95	$130.00
Purchase #7	$152.33	13.653%	$173.1276	$173.13	$173.15	$173.10
7 purchase totals =	$638.11		$690.3799	$690.39	$690.40	$690.40