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	$105.73	10.385%	$116.7101	$116.71	$116.70	$116.70
Purchase #2	$79.35	12.640%	$89.3798	$89.38	$89.40	$89.40
Purchase #3	$250.45	8.550%	$271.8635	$271.86	$271.85	$271.90
Purchase #4	$168.54	7.161%	$180.6091	$180.61	$180.60	$180.60
Purchase #5	$158.65	11.554%	$176.9804	$176.98	$177.00	$177.00
Purchase #6	$248.56	6.566%	$264.8804	$264.88	$264.90	$264.90
Purchase #7	$184.97	5.654%	$195.4282	$195.43	$195.45	$195.40
7 purchase totals =	$1,196.25		$1,295.8515	$1,295.85	$1,295.90	$1,295.90