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	$111.56	9.152%	$121.77	$121.77	$121.75	$121.80
Purchase #2	$37.38	12.448%	$42.0331	$42.03	$42.05	$42.00
Purchase #3	$136.94	5.373%	$144.2978	$144.30	$144.30	$144.30
Purchase #4	$85.92	12.172%	$96.3782	$96.38	$96.40	$96.40
Purchase #5	$116.38	7.205%	$124.7652	$124.77	$124.75	$124.80
Purchase #6	$150.30	12.451%	$169.0139	$169.01	$169.00	$169.00
Purchase #7	$223.46	10.745%	$247.4708	$247.47	$247.45	$247.50
7 purchase totals =	$861.94		$945.7290	$945.73	$945.70	$945.80