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	$71.42	13.334%	$80.9431	$80.94	$80.95	$80.90
Purchase #2	$112.72	13.587%	$128.0353	$128.04	$128.05	$128.00
Purchase #3	$178.83	11.735%	$199.8157	$199.82	$199.80	$199.80
Purchase #4	$175.30	7.477%	$188.4072	$188.41	$188.40	$188.40
Purchase #5	$38.77	4.674%	$40.5821	$40.58	$40.60	$40.60
Purchase #6	$187.49	12.263%	$210.4819	$210.48	$210.50	$210.50
Purchase #7	$29.51	7.487%	$31.7194	$31.72	$31.70	$31.70
7 purchase totals =	$794.04		$879.9847	$879.99	$880.00	$879.90