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	$135.30	11.262%	$150.5375	$150.54	$150.55	$150.50
Purchase #2	$187.52	8.466%	$203.3954	$203.40	$203.40	$203.40
Purchase #3	$111.57	7.476%	$119.911	$119.91	$119.90	$119.90
Purchase #4	$191.96	10.213%	$211.5649	$211.56	$211.55	$211.60
Purchase #5	$45.37	13.365%	$51.4337	$51.43	$51.45	$51.40
Purchase #6	$92.35	4.197%	$96.2259	$96.23	$96.25	$96.20
Purchase #7	$64.39	11.863%	$72.0286	$72.03	$72.05	$72.00
7 purchase totals =	$828.46		$905.0970	$905.10	$905.15	$905.00