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	$56.77	4.806%	$59.4984	$59.50	$59.50	$59.50
Purchase #2	$80.47	4.485%	$84.0791	$84.08	$84.10	$84.10
Purchase #3	$128.32	11.781%	$143.4374	$143.44	$143.45	$143.40
Purchase #4	$214.48	11.847%	$239.8894	$239.89	$239.90	$239.90
Purchase #5	$203.99	4.540%	$213.2511	$213.25	$213.25	$213.30
Purchase #6	$33.31	12.414%	$37.4451	$37.45	$37.45	$37.40
Purchase #7	$170.87	10.205%	$188.3073	$188.31	$188.30	$188.30
7 purchase totals =	$888.21		$965.9078	$965.92	$965.95	$965.90