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	$96.92	3.290%	$100.1087	$100.11	$100.10	$100.10
Purchase #2	$24.52	12.171%	$27.5043	$27.50	$27.50	$27.50
Purchase #3	$217.99	4.409%	$227.6012	$227.60	$227.60	$227.60
Purchase #4	$11.75	13.415%	$13.3263	$13.33	$13.35	$13.30
Purchase #5	$149.91	4.359%	$156.4446	$156.44	$156.45	$156.40
Purchase #6	$54.77	8.420%	$59.3816	$59.38	$59.40	$59.40
Purchase #7	$232.79	12.180%	$261.1438	$261.14	$261.15	$261.10
7 purchase totals =	$788.65		$845.5105	$845.50	$845.55	$845.40