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	$80.39	11.152%	$89.3551	$89.36	$89.35	$89.40
Purchase #2	$132.36	6.682%	$141.2043	$141.20	$141.20	$141.20
Purchase #3	$249.47	13.159%	$282.2978	$282.30	$282.30	$282.30
Purchase #4	$204.86	5.350%	$215.82	$215.82	$215.80	$215.80
Purchase #5	$191.55	4.326%	$199.8365	$199.84	$199.85	$199.80
Purchase #6	$178.37	12.571%	$200.7929	$200.79	$200.80	$200.80
Purchase #7	$135.70	3.342%	$140.2351	$140.24	$140.25	$140.20
7 purchase totals =	$1,172.70		$1,269.5417	$1,269.55	$1,269.55	$1,269.50