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	$96.89	6.393%	$103.0842	$103.08	$103.10	$103.10
Purchase #2	$236.61	12.409%	$265.9709	$265.97	$265.95	$266.00
Purchase #3	$7.36	5.514%	$7.7658	$7.77	$7.75	$7.80
Purchase #4	$103.54	12.464%	$116.4452	$116.45	$116.45	$116.40
Purchase #5	$169.78	9.126%	$185.2741	$185.27	$185.25	$185.30
Purchase #6	$231.51	12.853%	$261.266	$261.27	$261.25	$261.30
Purchase #7	$91.29	8.733%	$99.2624	$99.26	$99.25	$99.30
7 purchase totals =	$936.98		$1,039.0686	$1,039.07	$1,039.00	$1,039.20