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	$140.51	6.837%	$150.1167	$150.12	$150.10	$150.10
Purchase #2	$112.30	12.693%	$126.5542	$126.55	$126.55	$126.60
Purchase #3	$120.31	5.487%	$126.9114	$126.91	$126.90	$126.90
Purchase #4	$188.30	13.518%	$213.7544	$213.75	$213.75	$213.80
Purchase #5	$225.38	8.277%	$244.0347	$244.03	$244.05	$244.00
Purchase #6	$148.51	6.616%	$158.3354	$158.34	$158.35	$158.30
Purchase #7	$78.96	13.613%	$89.7088	$89.71	$89.70	$89.70
7 purchase totals =	$1,014.27		$1,109.4156	$1,109.41	$1,109.40	$1,109.40