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	$210.78	9.845%	$231.5313	$231.53	$231.55	$231.50
Purchase #2	$130.30	12.303%	$146.3308	$146.33	$146.35	$146.30
Purchase #3	$158.57	6.553%	$168.9611	$168.96	$168.95	$169.00
Purchase #4	$30.86	11.793%	$34.4993	$34.50	$34.50	$34.50
Purchase #5	$125.55	8.517%	$136.2431	$136.24	$136.25	$136.20
Purchase #6	$132.56	8.372%	$143.6579	$143.66	$143.65	$143.70
Purchase #7	$40.39	6.826%	$43.147	$43.15	$43.15	$43.10
7 purchase totals =	$829.01		$904.3705	$904.37	$904.40	$904.30