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	$82.66	8.635%	$89.7977	$89.80	$89.80	$89.80
Purchase #2	$204.37	8.422%	$221.582	$221.58	$221.60	$221.60
Purchase #3	$31.91	8.256%	$34.5445	$34.54	$34.55	$34.50
Purchase #4	$55.87	3.165%	$57.6383	$57.64	$57.65	$57.60
Purchase #5	$28.29	10.715%	$31.3213	$31.32	$31.30	$31.30
Purchase #6	$103.94	9.805%	$114.1313	$114.13	$114.15	$114.10
Purchase #7	$56.55	13.533%	$64.2029	$64.20	$64.20	$64.20
7 purchase totals =	$563.59		$613.2180	$613.21	$613.25	$613.10