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	$20.56	12.172%	$23.0626	$23.06	$23.05	$23.10
Purchase #2	$220.33	5.264%	$231.9282	$231.93	$231.95	$231.90
Purchase #3	$150.79	9.118%	$164.539	$164.54	$164.55	$164.50
Purchase #4	$26.77	10.149%	$29.4869	$29.49	$29.50	$29.50
Purchase #5	$100.31	11.609%	$111.955	$111.96	$111.95	$112.00
Purchase #6	$79.42	7.155%	$85.1025	$85.10	$85.10	$85.10
Purchase #7	$16.88	11.864%	$18.8826	$18.88	$18.90	$18.90
7 purchase totals =	$615.06		$664.9568	$664.96	$665.00	$665.00