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	$52.82	7.286%	$56.6685	$56.67	$56.65	$56.70
Purchase #2	$85.64	5.828%	$90.6311	$90.63	$90.65	$90.60
Purchase #3	$115.71	4.367%	$120.7631	$120.76	$120.75	$120.80
Purchase #4	$108.90	7.106%	$116.6384	$116.64	$116.65	$116.60
Purchase #5	$147.67	11.472%	$164.6107	$164.61	$164.60	$164.60
Purchase #6	$125.63	9.333%	$137.355	$137.36	$137.35	$137.40
Purchase #7	$84.28	11.807%	$94.2309	$94.23	$94.25	$94.20
7 purchase totals =	$720.65		$780.8977	$780.90	$780.90	$780.90