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	$79.34	5.161%	$83.4347	$83.43	$83.45	$83.40
Purchase #2	$54.25	6.301%	$57.6683	$57.67	$57.65	$57.70
Purchase #3	$243.27	9.190%	$265.6265	$265.63	$265.65	$265.60
Purchase #4	$88.26	11.727%	$98.6103	$98.61	$98.60	$98.60
Purchase #5	$178.59	3.325%	$184.5281	$184.53	$184.55	$184.50
Purchase #6	$84.80	5.556%	$89.5115	$89.51	$89.50	$89.50
Purchase #7	$124.77	5.816%	$132.0266	$132.03	$132.05	$132.00
7 purchase totals =	$853.28		$911.4060	$911.41	$911.45	$911.30