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	$72.28	11.496%	$80.5893	$80.59	$80.60	$80.60
Purchase #2	$22.69	8.348%	$24.5842	$24.58	$24.60	$24.60
Purchase #3	$104.42	4.459%	$109.0761	$109.08	$109.10	$109.10
Purchase #4	$104.72	7.137%	$112.1939	$112.19	$112.20	$112.20
Purchase #5	$181.95	4.182%	$189.5591	$189.56	$189.55	$189.60
Purchase #6	$36.80	12.705%	$41.4754	$41.48	$41.50	$41.50
Purchase #7	$226.42	10.183%	$249.4763	$249.48	$249.50	$249.50
7 purchase totals =	$749.28		$806.9543	$806.96	$807.05	$807.10