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	$66.48	10.650%	$73.5601	$73.56	$73.55	$73.60
Purchase #2	$66.96	7.189%	$71.7738	$71.77	$71.75	$71.80
Purchase #3	$157.58	5.485%	$166.2233	$166.22	$166.20	$166.20
Purchase #4	$153.72	6.676%	$163.9823	$163.98	$164.00	$164.00
Purchase #5	$79.64	13.735%	$90.5786	$90.58	$90.60	$90.60
Purchase #6	$128.44	8.629%	$139.5231	$139.52	$139.50	$139.50
Purchase #7	$245.62	7.609%	$264.3092	$264.31	$264.30	$264.30
7 purchase totals =	$898.44		$969.9504	$969.94	$969.90	$970.00