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	$131.47	6.709%	$140.2903	$140.29	$140.30	$140.30
Purchase #2	$206.95	10.367%	$228.4045	$228.40	$228.40	$228.40
Purchase #3	$74.78	10.553%	$82.6715	$82.67	$82.65	$82.70
Purchase #4	$143.99	10.209%	$158.6899	$158.69	$158.70	$158.70
Purchase #5	$122.46	12.610%	$137.9022	$137.90	$137.90	$137.90
Purchase #6	$80.80	6.234%	$85.8371	$85.84	$85.85	$85.80
Purchase #7	$250.62	7.675%	$269.8551	$269.86	$269.85	$269.90
7 purchase totals =	$1,011.07		$1,103.6506	$1,103.65	$1,103.65	$1,103.70