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	$22.74	5.244%	$23.9325	$23.93	$23.95	$23.90
Purchase #2	$249.80	4.460%	$260.9411	$260.94	$260.95	$260.90
Purchase #3	$72.89	10.721%	$80.7045	$80.70	$80.70	$80.70
Purchase #4	$57.30	4.487%	$59.8711	$59.87	$59.85	$59.90
Purchase #5	$51.60	8.179%	$55.8204	$55.82	$55.80	$55.80
Purchase #6	$175.96	5.726%	$186.0355	$186.04	$186.05	$186.00
Purchase #7	$42.28	7.406%	$45.4113	$45.41	$45.40	$45.40
7 purchase totals =	$672.57		$712.7164	$712.71	$712.70	$712.60