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	$30.85	9.793%	$33.8711	$33.87	$33.85	$33.90
Purchase #2	$201.30	8.318%	$218.0441	$218.04	$218.05	$218.00
Purchase #3	$30.89	7.633%	$33.2478	$33.25	$33.25	$33.20
Purchase #4	$108.81	5.428%	$114.7162	$114.72	$114.70	$114.70
Purchase #5	$36.40	3.624%	$37.7191	$37.72	$37.70	$37.70
Purchase #6	$170.83	12.324%	$191.8831	$191.88	$191.90	$191.90
Purchase #7	$116.72	10.213%	$128.6406	$128.64	$128.65	$128.60
7 purchase totals =	$695.80		$758.1220	$758.12	$758.10	$758.00