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	$109.38	13.112%	$123.7219	$123.72	$123.70	$123.70
Purchase #2	$122.36	7.316%	$131.3119	$131.31	$131.30	$131.30
Purchase #3	$49.34	13.680%	$56.0897	$56.09	$56.10	$56.10
Purchase #4	$21.54	4.287%	$22.4634	$22.46	$22.45	$22.50
Purchase #5	$129.33	11.575%	$144.2999	$144.30	$144.30	$144.30
Purchase #6	$162.30	10.772%	$179.783	$179.78	$179.80	$179.80
Purchase #7	$31.25	13.209%	$35.3778	$35.38	$35.40	$35.40
7 purchase totals =	$625.50		$693.0476	$693.04	$693.05	$693.10