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	$12.42	9.459%	$13.5948	$13.59	$13.60	$13.60
Purchase #2	$222.50	5.762%	$235.3205	$235.32	$235.30	$235.30
Purchase #3	$243.53	9.718%	$267.1962	$267.20	$267.20	$267.20
Purchase #4	$149.38	4.658%	$156.3381	$156.34	$156.35	$156.30
Purchase #5	$85.72	4.510%	$89.586	$89.59	$89.60	$89.60
Purchase #6	$11.89	9.598%	$13.0312	$13.03	$13.05	$13.00
Purchase #7	$134.39	12.324%	$150.9522	$150.95	$150.95	$151.00
7 purchase totals =	$859.83		$926.0190	$926.02	$926.05	$926.00