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	$120.53	9.385%	$131.8417	$131.84	$131.85	$131.80
Purchase #2	$205.54	3.769%	$213.2868	$213.29	$213.30	$213.30
Purchase #3	$44.30	10.724%	$49.0507	$49.05	$49.05	$49.10
Purchase #4	$82.46	8.171%	$89.1978	$89.20	$89.20	$89.20
Purchase #5	$10.83	13.855%	$12.3305	$12.33	$12.35	$12.30
Purchase #6	$245.65	8.311%	$266.066	$266.07	$266.05	$266.10
Purchase #7	$244.75	6.155%	$259.8144	$259.81	$259.80	$259.80
7 purchase totals =	$954.06		$1,021.5879	$1,021.59	$1,021.60	$1,021.60