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	$219.51	12.724%	$247.4405	$247.44	$247.45	$247.40
Purchase #2	$131.56	12.167%	$147.5669	$147.57	$147.55	$147.60
Purchase #3	$143.73	10.843%	$159.3146	$159.31	$159.30	$159.30
Purchase #4	$36.89	8.154%	$39.898	$39.90	$39.90	$39.90
Purchase #5	$173.68	6.523%	$185.0091	$185.01	$185.00	$185.00
Purchase #6	$53.47	5.259%	$56.282	$56.28	$56.30	$56.30
Purchase #7	$41.26	4.371%	$43.0635	$43.06	$43.05	$43.10
7 purchase totals =	$800.10		$878.5746	$878.57	$878.55	$878.60