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	$115.30	4.515%	$120.5058	$120.51	$120.50	$120.50
Purchase #2	$42.88	6.319%	$45.5896	$45.59	$45.60	$45.60
Purchase #3	$60.53	13.196%	$68.5175	$68.52	$68.50	$68.50
Purchase #4	$78.25	9.690%	$85.8324	$85.83	$85.85	$85.80
Purchase #5	$109.91	10.421%	$121.3637	$121.36	$121.35	$121.40
Purchase #6	$76.93	7.278%	$82.529	$82.53	$82.55	$82.50
Purchase #7	$36.38	9.216%	$39.7328	$39.73	$39.75	$39.70
7 purchase totals =	$520.18		$564.0708	$564.07	$564.10	$564.00