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	$139.57	12.351%	$156.8083	$156.81	$156.80	$156.80
Purchase #2	$58.54	12.774%	$66.0179	$66.02	$66.00	$66.00
Purchase #3	$89.58	7.520%	$96.3164	$96.32	$96.30	$96.30
Purchase #4	$175.47	12.567%	$197.5213	$197.52	$197.50	$197.50
Purchase #5	$226.30	8.438%	$245.3952	$245.40	$245.40	$245.40
Purchase #6	$144.62	10.364%	$159.6084	$159.61	$159.60	$159.60
Purchase #7	$76.79	5.317%	$80.8729	$80.87	$80.85	$80.90
7 purchase totals =	$910.87		$1,002.5404	$1,002.55	$1,002.45	$1,002.50