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	$249.99	10.368%	$275.909	$275.91	$275.90	$275.90
Purchase #2	$40.78	7.491%	$43.8348	$43.83	$43.85	$43.80
Purchase #3	$136.95	4.579%	$143.2209	$143.22	$143.20	$143.20
Purchase #4	$76.40	9.738%	$83.8398	$83.84	$83.85	$83.80
Purchase #5	$45.61	13.537%	$51.7842	$51.78	$51.80	$51.80
Purchase #6	$201.89	13.802%	$229.7549	$229.75	$229.75	$229.80
Purchase #7	$38.57	11.325%	$42.9381	$42.94	$42.95	$42.90
7 purchase totals =	$790.19		$871.2817	$871.27	$871.30	$871.20