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	$166.44	13.150%	$188.3269	$188.33	$188.35	$188.30
Purchase #2	$131.68	8.559%	$142.9505	$142.95	$142.95	$143.00
Purchase #3	$150.74	10.803%	$167.0244	$167.02	$167.00	$167.00
Purchase #4	$117.29	5.144%	$123.3234	$123.32	$123.30	$123.30
Purchase #5	$84.53	11.345%	$94.1199	$94.12	$94.10	$94.10
Purchase #6	$228.55	3.325%	$236.1493	$236.15	$236.15	$236.10
Purchase #7	$126.27	6.678%	$134.7023	$134.70	$134.70	$134.70
7 purchase totals =	$1,005.50		$1,086.5967	$1,086.59	$1,086.55	$1,086.50