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	$53.77	10.244%	$59.2782	$59.28	$59.30	$59.30
Purchase #2	$186.64	3.169%	$192.5546	$192.55	$192.55	$192.60
Purchase #3	$71.35	12.188%	$80.0461	$80.05	$80.05	$80.00
Purchase #4	$154.95	6.231%	$164.6049	$164.60	$164.60	$164.60
Purchase #5	$65.67	8.295%	$71.1173	$71.12	$71.10	$71.10
Purchase #6	$87.37	6.280%	$92.8568	$92.86	$92.85	$92.90
Purchase #7	$74.54	7.821%	$80.3698	$80.37	$80.35	$80.40
7 purchase totals =	$694.29		$740.8277	$740.83	$740.80	$740.90