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	$121.31	8.693%	$131.8555	$131.86	$131.85	$131.90
Purchase #2	$168.51	4.158%	$175.5166	$175.52	$175.50	$175.50
Purchase #3	$176.54	12.736%	$199.0241	$199.02	$199.00	$199.00
Purchase #4	$206.26	13.725%	$234.5692	$234.57	$234.55	$234.60
Purchase #5	$188.81	12.833%	$213.04	$213.04	$213.05	$213.00
Purchase #6	$249.35	11.665%	$278.4367	$278.44	$278.45	$278.40
Purchase #7	$78.65	13.272%	$89.0884	$89.09	$89.10	$89.10
7 purchase totals =	$1,189.43		$1,321.5305	$1,321.54	$1,321.50	$1,321.50