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	$36.83	6.585%	$39.2553	$39.26	$39.25	$39.30
Purchase #2	$41.33	3.593%	$42.815	$42.82	$42.80	$42.80
Purchase #3	$230.61	11.713%	$257.6213	$257.62	$257.60	$257.60
Purchase #4	$130.92	4.376%	$136.6491	$136.65	$136.65	$136.60
Purchase #5	$140.69	8.112%	$152.1028	$152.10	$152.10	$152.10
Purchase #6	$250.38	11.577%	$279.3665	$279.37	$279.35	$279.40
Purchase #7	$168.33	6.129%	$178.6469	$178.65	$178.65	$178.60
7 purchase totals =	$999.09		$1,086.4569	$1,086.47	$1,086.40	$1,086.40