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	$211.38	12.162%	$237.088	$237.09	$237.10	$237.10
Purchase #2	$135.96	9.256%	$148.5445	$148.54	$148.55	$148.50
Purchase #3	$47.32	13.755%	$53.8289	$53.83	$53.85	$53.80
Purchase #4	$126.64	10.706%	$140.1981	$140.20	$140.20	$140.20
Purchase #5	$106.79	4.798%	$111.9138	$111.91	$111.90	$111.90
Purchase #6	$55.76	3.155%	$57.5192	$57.52	$57.50	$57.50
Purchase #7	$137.85	13.760%	$156.8182	$156.82	$156.80	$156.80
7 purchase totals =	$821.70		$905.9107	$905.91	$905.90	$905.80