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	$127.55	5.268%	$134.2693	$134.27	$134.25	$134.30
Purchase #2	$91.76	3.305%	$94.7927	$94.79	$94.80	$94.80
Purchase #3	$107.84	4.720%	$112.93	$112.93	$112.95	$112.90
Purchase #4	$18.36	9.168%	$20.0432	$20.04	$20.05	$20.00
Purchase #5	$89.34	12.369%	$100.3905	$100.39	$100.40	$100.40
Purchase #6	$155.67	12.361%	$174.9124	$174.91	$174.90	$174.90
Purchase #7	$232.72	3.675%	$241.2725	$241.27	$241.25	$241.30
7 purchase totals =	$823.24		$878.6106	$878.60	$878.60	$878.60