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	$203.84	12.107%	$228.5189	$228.52	$228.50	$228.50
Purchase #2	$242.31	3.774%	$251.4548	$251.45	$251.45	$251.50
Purchase #3	$75.39	6.853%	$80.5565	$80.56	$80.55	$80.60
Purchase #4	$27.59	8.280%	$29.8745	$29.87	$29.85	$29.90
Purchase #5	$115.50	10.728%	$127.8908	$127.89	$127.90	$127.90
Purchase #6	$60.80	13.296%	$68.884	$68.88	$68.90	$68.90
Purchase #7	$72.64	10.663%	$80.3856	$80.39	$80.40	$80.40
7 purchase totals =	$798.07		$867.5651	$867.56	$867.55	$867.70