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	$45.25	10.200%	$49.8655	$49.87	$49.85	$49.90
Purchase #2	$184.52	6.400%	$196.3293	$196.33	$196.35	$196.30
Purchase #3	$242.73	12.706%	$273.5713	$273.57	$273.55	$273.60
Purchase #4	$90.61	4.476%	$94.6657	$94.67	$94.65	$94.70
Purchase #5	$8.72	9.839%	$9.578	$9.58	$9.60	$9.60
Purchase #6	$59.67	9.106%	$65.1036	$65.10	$65.10	$65.10
Purchase #7	$234.53	9.296%	$256.3319	$256.33	$256.35	$256.30
7 purchase totals =	$866.03		$945.4453	$945.45	$945.45	$945.50