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	$28.87	4.403%	$30.1411	$30.14	$30.15	$30.10
Purchase #2	$82.45	3.765%	$85.5542	$85.55	$85.55	$85.60
Purchase #3	$77.86	10.280%	$85.864	$85.86	$85.85	$85.90
Purchase #4	$182.84	3.357%	$188.9779	$188.98	$189.00	$189.00
Purchase #5	$127.59	13.826%	$145.2306	$145.23	$145.25	$145.20
Purchase #6	$161.41	8.365%	$174.9119	$174.91	$174.90	$174.90
Purchase #7	$207.58	12.348%	$233.212	$233.21	$233.20	$233.20
7 purchase totals =	$868.60		$943.8917	$943.88	$943.90	$943.90