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	$20.38	7.228%	$21.8531	$21.85	$21.85	$21.90
Purchase #2	$50.68	5.413%	$53.4233	$53.42	$53.40	$53.40
Purchase #3	$167.46	5.369%	$176.4509	$176.45	$176.45	$176.50
Purchase #4	$68.61	6.310%	$72.9393	$72.94	$72.95	$72.90
Purchase #5	$159.94	12.168%	$179.4015	$179.40	$179.40	$179.40
Purchase #6	$54.40	8.862%	$59.2209	$59.22	$59.20	$59.20
Purchase #7	$91.41	13.376%	$103.637	$103.64	$103.65	$103.60
7 purchase totals =	$612.88		$666.9260	$666.92	$666.90	$666.90