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	$79.85	5.713%	$84.4118	$84.41	$84.40	$84.40
Purchase #2	$96.25	9.304%	$105.2051	$105.21	$105.20	$105.20
Purchase #3	$50.31	4.772%	$52.7108	$52.71	$52.70	$52.70
Purchase #4	$187.67	6.490%	$199.8498	$199.85	$199.85	$199.80
Purchase #5	$182.49	9.322%	$199.5017	$199.50	$199.50	$199.50
Purchase #6	$199.91	11.228%	$222.3559	$222.36	$222.35	$222.40
Purchase #7	$106.39	7.454%	$114.3203	$114.32	$114.30	$114.30
7 purchase totals =	$902.87		$978.3554	$978.36	$978.30	$978.30