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	$126.36	10.646%	$139.8123	$139.81	$139.80	$139.80
Purchase #2	$230.56	5.784%	$243.8956	$243.90	$243.90	$243.90
Purchase #3	$133.59	13.260%	$151.304	$151.30	$151.30	$151.30
Purchase #4	$25.70	6.410%	$27.3474	$27.35	$27.35	$27.30
Purchase #5	$144.33	4.377%	$150.6473	$150.65	$150.65	$150.60
Purchase #6	$20.68	13.559%	$23.484	$23.48	$23.50	$23.50
Purchase #7	$46.57	11.411%	$51.8841	$51.88	$51.90	$51.90
7 purchase totals =	$727.79		$788.3747	$788.37	$788.40	$788.30