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	$241.82	13.218%	$273.7838	$273.78	$273.80	$273.80
Purchase #2	$56.29	5.241%	$59.2402	$59.24	$59.25	$59.20
Purchase #3	$198.52	13.447%	$225.215	$225.22	$225.20	$225.20
Purchase #4	$63.78	13.320%	$72.2755	$72.28	$72.30	$72.30
Purchase #5	$73.55	10.789%	$81.4853	$81.49	$81.50	$81.50
Purchase #6	$196.92	6.244%	$209.2157	$209.22	$209.20	$209.20
Purchase #7	$108.50	10.258%	$119.6299	$119.63	$119.65	$119.60
7 purchase totals =	$939.38		$1,040.8454	$1,040.86	$1,040.90	$1,040.80