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	$247.85	12.390%	$278.5586	$278.56	$278.55	$278.60
Purchase #2	$40.48	10.156%	$44.5911	$44.59	$44.60	$44.60
Purchase #3	$96.51	3.775%	$100.1533	$100.15	$100.15	$100.20
Purchase #4	$77.49	9.148%	$84.5788	$84.58	$84.60	$84.60
Purchase #5	$193.56	8.260%	$209.5481	$209.55	$209.55	$209.50
Purchase #6	$196.60	13.246%	$222.6416	$222.64	$222.65	$222.60
Purchase #7	$243.39	7.120%	$260.7194	$260.72	$260.70	$260.70
7 purchase totals =	$1,095.88		$1,200.7909	$1,200.79	$1,200.80	$1,200.80