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	$55.90	10.553%	$61.7991	$61.80	$61.80	$61.80
Purchase #2	$215.60	6.118%	$228.7904	$228.79	$228.80	$228.80
Purchase #3	$150.32	10.727%	$166.4448	$166.44	$166.45	$166.40
Purchase #4	$205.75	13.742%	$234.0242	$234.02	$234.00	$234.00
Purchase #5	$70.38	3.480%	$72.8292	$72.83	$72.85	$72.80
Purchase #6	$34.45	7.348%	$36.9814	$36.98	$37.00	$37.00
Purchase #7	$162.25	12.610%	$182.7097	$182.71	$182.70	$182.70
7 purchase totals =	$894.65		$983.5788	$983.57	$983.60	$983.50