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	$249.63	9.559%	$273.4921	$273.49	$273.50	$273.50
Purchase #2	$178.47	6.721%	$190.465	$190.47	$190.45	$190.50
Purchase #3	$238.56	10.797%	$264.3173	$264.32	$264.30	$264.30
Purchase #4	$154.47	7.195%	$165.5841	$165.58	$165.60	$165.60
Purchase #5	$63.42	8.610%	$68.8805	$68.88	$68.90	$68.90
Purchase #6	$100.87	6.805%	$107.7342	$107.73	$107.75	$107.70
Purchase #7	$51.27	12.705%	$57.7839	$57.78	$57.80	$57.80
7 purchase totals =	$1,036.69		$1,128.2571	$1,128.25	$1,128.30	$1,128.30