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	$134.97	7.344%	$144.8822	$144.88	$144.90	$144.90
Purchase #2	$47.76	13.564%	$54.2382	$54.24	$54.25	$54.20
Purchase #3	$153.53	9.835%	$168.6297	$168.63	$168.65	$168.60
Purchase #4	$104.27	7.375%	$111.9599	$111.96	$111.95	$112.00
Purchase #5	$85.26	5.240%	$89.7276	$89.73	$89.75	$89.70
Purchase #6	$151.95	8.531%	$164.9129	$164.91	$164.90	$164.90
Purchase #7	$214.95	7.838%	$231.7978	$231.80	$231.80	$231.80
7 purchase totals =	$892.69		$966.1483	$966.15	$966.20	$966.10