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	$116.83	9.121%	$127.4861	$127.49	$127.50	$127.50
Purchase #2	$200.86	12.389%	$225.7445	$225.74	$225.75	$225.70
Purchase #3	$160.88	6.479%	$171.3034	$171.30	$171.30	$171.30
Purchase #4	$156.38	6.715%	$166.8809	$166.88	$166.90	$166.90
Purchase #5	$99.55	10.332%	$109.8355	$109.84	$109.85	$109.80
Purchase #6	$50.69	4.869%	$53.1581	$53.16	$53.15	$53.20
Purchase #7	$214.55	8.354%	$232.4735	$232.47	$232.45	$232.50
7 purchase totals =	$999.74		$1,086.8820	$1,086.88	$1,086.90	$1,086.90