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	$59.80	7.855%	$64.4973	$64.50	$64.50	$64.50
Purchase #2	$81.94	10.841%	$90.8231	$90.82	$90.80	$90.80
Purchase #3	$134.59	12.510%	$151.4272	$151.43	$151.45	$151.40
Purchase #4	$121.81	5.543%	$128.5619	$128.56	$128.55	$128.60
Purchase #5	$199.76	8.350%	$216.44	$216.44	$216.45	$216.40
Purchase #6	$178.62	11.113%	$198.47	$198.47	$198.45	$198.50
Purchase #7	$105.91	6.241%	$112.5198	$112.52	$112.50	$112.50
7 purchase totals =	$882.43		$962.7393	$962.74	$962.70	$962.70