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	$43.65	4.351%	$45.5492	$45.55	$45.55	$45.50
Purchase #2	$103.41	3.712%	$107.2486	$107.25	$107.25	$107.20
Purchase #3	$232.53	7.587%	$250.1721	$250.17	$250.15	$250.20
Purchase #4	$57.70	4.191%	$60.1182	$60.12	$60.10	$60.10
Purchase #5	$51.90	4.442%	$54.2054	$54.21	$54.20	$54.20
Purchase #6	$27.56	6.867%	$29.4525	$29.45	$29.45	$29.50
Purchase #7	$89.93	12.131%	$100.8394	$100.84	$100.85	$100.80
7 purchase totals =	$606.68		$647.5854	$647.59	$647.55	$647.50