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	$43.49	13.232%	$49.2446	$49.24	$49.25	$49.20
Purchase #2	$108.82	10.223%	$119.9447	$119.94	$119.95	$119.90
Purchase #3	$160.95	5.217%	$169.3468	$169.35	$169.35	$169.30
Purchase #4	$42.69	7.483%	$45.8845	$45.88	$45.90	$45.90
Purchase #5	$196.57	7.150%	$210.6248	$210.62	$210.60	$210.60
Purchase #6	$122.27	12.369%	$137.3936	$137.39	$137.40	$137.40
Purchase #7	$33.91	11.629%	$37.8534	$37.85	$37.85	$37.90
7 purchase totals =	$708.70		$770.2924	$770.27	$770.30	$770.20