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	$114.89	11.794%	$128.4401	$128.44	$128.45	$128.40
Purchase #2	$82.38	7.693%	$88.7175	$88.72	$88.70	$88.70
Purchase #3	$86.94	10.789%	$96.32	$96.32	$96.30	$96.30
Purchase #4	$98.28	10.377%	$108.4785	$108.48	$108.50	$108.50
Purchase #5	$31.67	8.178%	$34.26	$34.26	$34.25	$34.30
Purchase #6	$54.99	9.240%	$60.0711	$60.07	$60.05	$60.10
Purchase #7	$90.86	13.238%	$102.888	$102.89	$102.90	$102.90
7 purchase totals =	$560.01		$619.1752	$619.18	$619.15	$619.20