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	$46.52	11.553%	$51.8945	$51.89	$51.90	$51.90
Purchase #2	$104.40	9.336%	$114.1468	$114.15	$114.15	$114.10
Purchase #3	$83.91	7.741%	$90.4055	$90.41	$90.40	$90.40
Purchase #4	$160.62	5.156%	$168.9016	$168.90	$168.90	$168.90
Purchase #5	$157.92	10.301%	$174.1873	$174.19	$174.20	$174.20
Purchase #6	$206.47	6.668%	$220.2374	$220.24	$220.25	$220.20
Purchase #7	$84.37	6.719%	$90.0388	$90.04	$90.05	$90.00
7 purchase totals =	$844.21		$909.8119	$909.82	$909.85	$909.70