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	$16.77	7.570%	$18.0395	$18.04	$18.05	$18.00
Purchase #2	$196.38	10.226%	$216.4618	$216.46	$216.45	$216.50
Purchase #3	$82.25	7.170%	$88.1473	$88.15	$88.15	$88.10
Purchase #4	$35.77	10.597%	$39.5605	$39.56	$39.55	$39.60
Purchase #5	$88.49	13.152%	$100.1282	$100.13	$100.15	$100.10
Purchase #6	$23.60	9.602%	$25.8661	$25.87	$25.85	$25.90
Purchase #7	$168.42	12.785%	$189.9525	$189.95	$189.95	$190.00
7 purchase totals =	$611.68		$678.1559	$678.16	$678.15	$678.20