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	$21.55	7.839%	$23.2393	$23.24	$23.25	$23.20
Purchase #2	$43.34	13.359%	$49.1298	$49.13	$49.15	$49.10
Purchase #3	$56.81	4.392%	$59.3051	$59.31	$59.30	$59.30
Purchase #4	$200.57	6.604%	$213.8156	$213.82	$213.80	$213.80
Purchase #5	$139.87	3.596%	$144.8997	$144.90	$144.90	$144.90
Purchase #6	$172.29	13.816%	$196.0936	$196.09	$196.10	$196.10
Purchase #7	$122.74	8.476%	$133.1434	$133.14	$133.15	$133.10
7 purchase totals =	$757.17		$819.6265	$819.63	$819.65	$819.50