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	$19.58	11.475%	$21.8268	$21.83	$21.85	$21.80
Purchase #2	$37.70	8.358%	$40.851	$40.85	$40.85	$40.90
Purchase #3	$38.91	5.324%	$40.9816	$40.98	$41.00	$41.00
Purchase #4	$164.25	10.524%	$181.5357	$181.54	$181.55	$181.50
Purchase #5	$80.41	10.551%	$88.8941	$88.89	$88.90	$88.90
Purchase #6	$134.61	7.226%	$144.3369	$144.34	$144.35	$144.30
Purchase #7	$134.36	9.271%	$146.8165	$146.82	$146.80	$146.80
7 purchase totals =	$609.82		$665.2426	$665.25	$665.30	$665.20