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	$16.30	11.432%	$18.1634	$18.16	$18.15	$18.20
Purchase #2	$49.85	6.550%	$53.1152	$53.12	$53.10	$53.10
Purchase #3	$169.56	9.409%	$185.5139	$185.51	$185.50	$185.50
Purchase #4	$128.30	11.311%	$142.812	$142.81	$142.80	$142.80
Purchase #5	$73.98	3.481%	$76.5552	$76.56	$76.55	$76.60
Purchase #6	$36.42	7.786%	$39.2557	$39.26	$39.25	$39.30
Purchase #7	$64.39	10.811%	$71.3512	$71.35	$71.35	$71.40
7 purchase totals =	$538.80		$586.7666	$586.77	$586.70	$586.90