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	$170.59	11.240%	$189.7643	$189.76	$189.75	$189.80
Purchase #2	$200.37	10.554%	$221.517	$221.52	$221.50	$221.50
Purchase #3	$200.41	12.686%	$225.834	$225.83	$225.85	$225.80
Purchase #4	$111.81	8.678%	$121.5129	$121.51	$121.50	$121.50
Purchase #5	$132.56	7.152%	$142.0407	$142.04	$142.05	$142.00
Purchase #6	$229.73	12.296%	$257.9776	$257.98	$258.00	$258.00
Purchase #7	$215.58	4.780%	$225.8847	$225.88	$225.90	$225.90
7 purchase totals =	$1,261.05		$1,384.5312	$1,384.52	$1,384.55	$1,384.50