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	$120.87	6.573%	$128.8148	$128.81	$128.80	$128.80
Purchase #2	$248.87	10.703%	$275.5066	$275.51	$275.50	$275.50
Purchase #3	$86.74	4.731%	$90.8437	$90.84	$90.85	$90.80
Purchase #4	$130.32	8.849%	$141.852	$141.85	$141.85	$141.90
Purchase #5	$128.89	9.396%	$141.0005	$141.00	$141.00	$141.00
Purchase #6	$56.59	11.148%	$62.8987	$62.90	$62.90	$62.90
Purchase #7	$140.81	5.501%	$148.556	$148.56	$148.55	$148.60
7 purchase totals =	$913.09		$989.4723	$989.47	$989.45	$989.50