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	$222.61	4.136%	$231.8171	$231.82	$231.80	$231.80
Purchase #2	$198.45	12.198%	$222.6569	$222.66	$222.65	$222.70
Purchase #3	$243.89	9.611%	$267.3303	$267.33	$267.35	$267.30
Purchase #4	$127.55	12.451%	$143.4313	$143.43	$143.45	$143.40
Purchase #5	$105.66	8.706%	$114.8588	$114.86	$114.85	$114.90
Purchase #6	$74.71	7.802%	$80.5389	$80.54	$80.55	$80.50
Purchase #7	$89.80	12.302%	$100.8472	$100.85	$100.85	$100.80
7 purchase totals =	$1,062.67		$1,161.4805	$1,161.49	$1,161.50	$1,161.40