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	$47.85	13.114%	$54.125	$54.13	$54.15	$54.10
Purchase #2	$147.51	8.211%	$159.622	$159.62	$159.60	$159.60
Purchase #3	$38.67	4.159%	$40.2783	$40.28	$40.30	$40.30
Purchase #4	$37.34	3.357%	$38.5935	$38.59	$38.60	$38.60
Purchase #5	$151.69	7.238%	$162.6693	$162.67	$162.65	$162.70
Purchase #6	$174.47	11.417%	$194.3892	$194.39	$194.40	$194.40
Purchase #7	$242.32	3.257%	$250.2124	$250.21	$250.20	$250.20
7 purchase totals =	$839.85		$899.8897	$899.89	$899.90	$899.90