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	$235.81	8.534%	$255.934	$255.93	$255.95	$255.90
Purchase #2	$169.38	7.771%	$182.5425	$182.54	$182.55	$182.50
Purchase #3	$131.69	3.321%	$136.0634	$136.06	$136.05	$136.10
Purchase #4	$144.83	9.556%	$158.67	$158.67	$158.65	$158.70
Purchase #5	$51.81	11.624%	$57.8324	$57.83	$57.85	$57.80
Purchase #6	$165.27	10.157%	$182.0565	$182.06	$182.05	$182.10
Purchase #7	$178.56	4.348%	$186.3238	$186.32	$186.30	$186.30
7 purchase totals =	$1,077.35		$1,159.4226	$1,159.41	$1,159.40	$1,159.40