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	$67.77	9.868%	$74.4575	$74.46	$74.45	$74.50
Purchase #2	$70.95	10.840%	$78.641	$78.64	$78.65	$78.60
Purchase #3	$123.81	6.760%	$132.1796	$132.18	$132.20	$132.20
Purchase #4	$241.95	9.538%	$265.0272	$265.03	$265.05	$265.00
Purchase #5	$210.38	10.743%	$232.9811	$232.98	$233.00	$233.00
Purchase #6	$57.39	7.522%	$61.7069	$61.71	$61.70	$61.70
Purchase #7	$99.59	12.355%	$111.8943	$111.89	$111.90	$111.90
7 purchase totals =	$871.84		$956.8876	$956.89	$956.95	$956.90