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	$81.38	9.523%	$89.1298	$89.13	$89.15	$89.10
Purchase #2	$228.68	5.497%	$241.2505	$241.25	$241.25	$241.30
Purchase #3	$187.83	4.625%	$196.5171	$196.52	$196.50	$196.50
Purchase #4	$112.74	12.548%	$126.8866	$126.89	$126.90	$126.90
Purchase #5	$176.83	12.447%	$198.84	$198.84	$198.85	$198.80
Purchase #6	$46.29	4.772%	$48.499	$48.50	$48.50	$48.50
Purchase #7	$47.67	4.109%	$49.6288	$49.63	$49.65	$49.60
7 purchase totals =	$881.42		$950.7518	$950.76	$950.80	$950.70