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	$84.80	5.546%	$89.503	$89.50	$89.50	$89.50
Purchase #2	$137.88	11.807%	$154.1595	$154.16	$154.15	$154.20
Purchase #3	$212.71	13.117%	$240.6112	$240.61	$240.60	$240.60
Purchase #4	$250.32	3.300%	$258.5806	$258.58	$258.60	$258.60
Purchase #5	$32.66	12.118%	$36.6177	$36.62	$36.60	$36.60
Purchase #6	$129.77	4.262%	$135.3008	$135.30	$135.30	$135.30
Purchase #7	$66.27	7.845%	$71.4689	$71.47	$71.45	$71.50
7 purchase totals =	$914.41		$986.2417	$986.24	$986.20	$986.30