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	$50.84	5.552%	$53.6626	$53.66	$53.65	$53.70
Purchase #2	$224.85	3.365%	$232.4162	$232.42	$232.40	$232.40
Purchase #3	$60.76	9.687%	$66.6458	$66.65	$66.65	$66.60
Purchase #4	$41.37	9.228%	$45.1876	$45.19	$45.20	$45.20
Purchase #5	$42.58	12.481%	$47.8944	$47.89	$47.90	$47.90
Purchase #6	$51.29	4.154%	$53.4206	$53.42	$53.40	$53.40
Purchase #7	$100.47	3.206%	$103.6911	$103.69	$103.70	$103.70
7 purchase totals =	$572.16		$602.9183	$602.92	$602.90	$602.90