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	$5.89	11.799%	$6.585	$6.59	$6.60	$6.60
Purchase #2	$53.51	11.738%	$59.791	$59.79	$59.80	$59.80
Purchase #3	$172.90	6.595%	$184.3028	$184.30	$184.30	$184.30
Purchase #4	$214.44	9.737%	$235.32	$235.32	$235.30	$235.30
Purchase #5	$53.78	10.147%	$59.2371	$59.24	$59.25	$59.20
Purchase #6	$193.51	5.442%	$204.0408	$204.04	$204.05	$204.00
Purchase #7	$26.60	3.489%	$27.5281	$27.53	$27.55	$27.50
7 purchase totals =	$720.63		$776.8048	$776.81	$776.85	$776.70