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	$242.87	11.786%	$271.4947	$271.49	$271.50	$271.50
Purchase #2	$6.50	10.441%	$7.1787	$7.18	$7.20	$7.20
Purchase #3	$58.28	13.505%	$66.1507	$66.15	$66.15	$66.20
Purchase #4	$249.98	11.655%	$279.1152	$279.12	$279.10	$279.10
Purchase #5	$238.44	8.851%	$259.5443	$259.54	$259.55	$259.50
Purchase #6	$80.42	6.314%	$85.4977	$85.50	$85.50	$85.50
Purchase #7	$45.66	10.377%	$50.3981	$50.40	$50.40	$50.40
7 purchase totals =	$922.15		$1,019.3794	$1,019.38	$1,019.40	$1,019.40