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	$55.93	9.775%	$61.3972	$61.40	$61.40	$61.40
Purchase #2	$144.69	3.849%	$150.2591	$150.26	$150.25	$150.30
Purchase #3	$238.76	13.199%	$270.2739	$270.27	$270.25	$270.30
Purchase #4	$94.44	3.592%	$97.8323	$97.83	$97.85	$97.80
Purchase #5	$64.26	12.706%	$72.4249	$72.42	$72.40	$72.40
Purchase #6	$136.33	6.427%	$145.0919	$145.09	$145.10	$145.10
Purchase #7	$109.38	12.614%	$123.1772	$123.18	$123.20	$123.20
7 purchase totals =	$843.79		$920.4565	$920.45	$920.45	$920.50