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	$168.33	9.604%	$184.4964	$184.50	$184.50	$184.50
Purchase #2	$30.93	11.688%	$34.5451	$34.55	$34.55	$34.50
Purchase #3	$203.52	12.108%	$228.1622	$228.16	$228.15	$228.20
Purchase #4	$182.35	11.830%	$203.922	$203.92	$203.90	$203.90
Purchase #5	$72.52	13.611%	$82.3907	$82.39	$82.40	$82.40
Purchase #6	$116.93	9.149%	$127.6279	$127.63	$127.65	$127.60
Purchase #7	$236.57	12.203%	$265.4386	$265.44	$265.45	$265.40
7 purchase totals =	$1,011.15		$1,126.5829	$1,126.59	$1,126.60	$1,126.50