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	$37.76	9.612%	$41.3895	$41.39	$41.40	$41.40
Purchase #2	$107.72	9.462%	$117.9125	$117.91	$117.90	$117.90
Purchase #3	$34.32	4.147%	$35.7433	$35.74	$35.75	$35.70
Purchase #4	$74.59	3.564%	$77.2484	$77.25	$77.25	$77.20
Purchase #5	$37.48	10.659%	$41.475	$41.48	$41.50	$41.50
Purchase #6	$33.27	3.869%	$34.5572	$34.56	$34.55	$34.60
Purchase #7	$139.75	3.826%	$145.0968	$145.10	$145.10	$145.10
7 purchase totals =	$464.89		$493.4227	$493.43	$493.45	$493.40