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	$35.54	11.418%	$39.598	$39.60	$39.60	$39.60
Purchase #2	$199.38	5.502%	$210.3499	$210.35	$210.35	$210.30
Purchase #3	$78.44	7.461%	$84.2924	$84.29	$84.30	$84.30
Purchase #4	$54.31	9.526%	$59.4836	$59.48	$59.50	$59.50
Purchase #5	$45.44	13.293%	$51.4803	$51.48	$51.50	$51.50
Purchase #6	$196.60	6.788%	$209.9452	$209.95	$209.95	$209.90
Purchase #7	$29.49	5.340%	$31.0648	$31.06	$31.05	$31.10
7 purchase totals =	$639.20		$686.2142	$686.21	$686.25	$686.20