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	$185.71	11.182%	$206.4761	$206.48	$206.50	$206.50
Purchase #2	$59.76	13.721%	$67.9597	$67.96	$67.95	$68.00
Purchase #3	$49.96	9.868%	$54.8901	$54.89	$54.90	$54.90
Purchase #4	$31.72	10.701%	$35.1144	$35.11	$35.10	$35.10
Purchase #5	$14.97	5.747%	$15.8303	$15.83	$15.85	$15.80
Purchase #6	$129.62	7.363%	$139.1639	$139.16	$139.15	$139.20
Purchase #7	$139.71	13.473%	$158.5331	$158.53	$158.55	$158.50
7 purchase totals =	$611.45		$677.9676	$677.96	$678.00	$678.00