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	$111.34	11.309%	$123.9314	$123.93	$123.95	$123.90
Purchase #2	$112.33	5.621%	$118.6441	$118.64	$118.65	$118.60
Purchase #3	$29.51	4.555%	$30.8542	$30.85	$30.85	$30.90
Purchase #4	$38.53	10.858%	$42.7136	$42.71	$42.70	$42.70
Purchase #5	$40.68	9.721%	$44.6345	$44.63	$44.65	$44.60
Purchase #6	$61.83	12.830%	$69.7628	$69.76	$69.75	$69.80
Purchase #7	$229.89	12.682%	$259.0446	$259.04	$259.05	$259.00
7 purchase totals =	$624.11		$689.5852	$689.56	$689.60	$689.50