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	$54.40	6.209%	$57.7777	$57.78	$57.80	$57.80
Purchase #2	$32.91	3.443%	$34.0431	$34.04	$34.05	$34.00
Purchase #3	$102.81	7.622%	$110.6462	$110.65	$110.65	$110.60
Purchase #4	$93.87	7.765%	$101.159	$101.16	$101.15	$101.20
Purchase #5	$148.61	12.621%	$167.3661	$167.37	$167.35	$167.40
Purchase #6	$34.43	3.187%	$35.5273	$35.53	$35.55	$35.50
Purchase #7	$75.32	4.179%	$78.4676	$78.47	$78.45	$78.50
7 purchase totals =	$542.35		$584.9870	$585.00	$585.00	$585.00