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	$45.39	13.819%	$51.6624	$51.66	$51.65	$51.70
Purchase #2	$241.66	3.471%	$250.048	$250.05	$250.05	$250.00
Purchase #3	$177.63	12.221%	$199.3382	$199.34	$199.35	$199.30
Purchase #4	$123.50	4.346%	$128.8673	$128.87	$128.85	$128.90
Purchase #5	$77.39	11.546%	$86.3254	$86.33	$86.35	$86.30
Purchase #6	$58.32	12.664%	$65.7056	$65.71	$65.70	$65.70
Purchase #7	$35.38	5.673%	$37.3871	$37.39	$37.40	$37.40
7 purchase totals =	$759.27		$819.3340	$819.35	$819.35	$819.30