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	$135.85	10.794%	$150.5136	$150.51	$150.50	$150.50
Purchase #2	$68.57	12.293%	$76.9993	$77.00	$77.00	$77.00
Purchase #3	$111.90	10.124%	$123.2288	$123.23	$123.25	$123.20
Purchase #4	$38.36	3.336%	$39.6397	$39.64	$39.65	$39.60
Purchase #5	$181.93	4.214%	$189.5965	$189.60	$189.60	$189.60
Purchase #6	$164.64	4.345%	$171.7936	$171.79	$171.80	$171.80
Purchase #7	$215.28	4.823%	$225.663	$225.66	$225.65	$225.70
7 purchase totals =	$916.53		$977.4345	$977.43	$977.45	$977.40