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	$17.39	4.717%	$18.2103	$18.21	$18.20	$18.20
Purchase #2	$142.44	5.484%	$150.2514	$150.25	$150.25	$150.30
Purchase #3	$120.59	10.379%	$133.106	$133.11	$133.10	$133.10
Purchase #4	$13.80	12.387%	$15.5094	$15.51	$15.50	$15.50
Purchase #5	$116.26	6.587%	$123.918	$123.92	$123.90	$123.90
Purchase #6	$109.28	6.136%	$115.9854	$115.99	$116.00	$116.00
Purchase #7	$227.69	7.122%	$243.9061	$243.91	$243.90	$243.90
7 purchase totals =	$747.45		$800.8866	$800.90	$800.85	$800.90