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	$27.76	12.307%	$31.1764	$31.18	$31.20	$31.20
Purchase #2	$60.53	5.737%	$64.0026	$64.00	$64.00	$64.00
Purchase #3	$194.89	13.683%	$221.5568	$221.56	$221.55	$221.60
Purchase #4	$168.72	10.348%	$186.1791	$186.18	$186.20	$186.20
Purchase #5	$102.63	4.722%	$107.4762	$107.48	$107.50	$107.50
Purchase #6	$100.82	10.717%	$111.6249	$111.62	$111.60	$111.60
Purchase #7	$147.98	13.609%	$168.1186	$168.12	$168.10	$168.10
7 purchase totals =	$803.33		$890.1346	$890.14	$890.15	$890.20