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	$130.78	6.137%	$138.806	$138.81	$138.80	$138.80
Purchase #2	$131.73	11.839%	$147.3255	$147.33	$147.35	$147.30
Purchase #3	$134.86	5.762%	$142.6306	$142.63	$142.65	$142.60
Purchase #4	$74.80	10.465%	$82.6278	$82.63	$82.65	$82.60
Purchase #5	$91.81	12.167%	$102.9805	$102.98	$103.00	$103.00
Purchase #6	$38.87	9.838%	$42.694	$42.69	$42.70	$42.70
Purchase #7	$69.99	11.781%	$78.2355	$78.24	$78.25	$78.20
7 purchase totals =	$672.84		$735.2999	$735.31	$735.40	$735.20