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	$25.72	6.248%	$27.327	$27.33	$27.35	$27.30
Purchase #2	$226.51	11.856%	$253.365	$253.37	$253.35	$253.40
Purchase #3	$54.90	10.691%	$60.7694	$60.77	$60.75	$60.80
Purchase #4	$132.88	10.315%	$146.5866	$146.59	$146.60	$146.60
Purchase #5	$62.32	7.686%	$67.1099	$67.11	$67.10	$67.10
Purchase #6	$104.81	3.143%	$108.1042	$108.10	$108.10	$108.10
Purchase #7	$65.93	9.435%	$72.1505	$72.15	$72.15	$72.20
7 purchase totals =	$673.07		$735.4126	$735.42	$735.40	$735.50