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	$84.56	7.290%	$90.7244	$90.72	$90.70	$90.70
Purchase #2	$49.91	11.576%	$55.6876	$55.69	$55.70	$55.70
Purchase #3	$133.35	3.215%	$137.6372	$137.64	$137.65	$137.60
Purchase #4	$53.89	12.622%	$60.692	$60.69	$60.70	$60.70
Purchase #5	$198.95	4.346%	$207.5964	$207.60	$207.60	$207.60
Purchase #6	$150.33	11.345%	$167.3849	$167.38	$167.40	$167.40
Purchase #7	$92.33	11.401%	$102.8565	$102.86	$102.85	$102.90
7 purchase totals =	$763.32		$822.5790	$822.58	$822.60	$822.60