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	$17.43	6.237%	$18.5171	$18.52	$18.50	$18.50
Purchase #2	$197.61	12.668%	$222.6432	$222.64	$222.65	$222.60
Purchase #3	$186.46	6.151%	$197.9292	$197.93	$197.95	$197.90
Purchase #4	$111.93	13.625%	$127.1805	$127.18	$127.20	$127.20
Purchase #5	$206.81	10.145%	$227.7909	$227.79	$227.80	$227.80
Purchase #6	$193.39	13.511%	$219.5189	$219.52	$219.50	$219.50
Purchase #7	$9.78	4.659%	$10.2357	$10.24	$10.25	$10.20
7 purchase totals =	$923.41		$1,023.8155	$1,023.82	$1,023.85	$1,023.70