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	$227.91	6.864%	$243.5537	$243.55	$243.55	$243.60
Purchase #2	$134.34	5.561%	$141.8106	$141.81	$141.80	$141.80
Purchase #3	$60.29	3.445%	$62.367	$62.37	$62.35	$62.40
Purchase #4	$107.98	10.664%	$119.495	$119.50	$119.50	$119.50
Purchase #5	$104.90	13.872%	$119.4517	$119.45	$119.45	$119.50
Purchase #6	$47.27	9.841%	$51.9218	$51.92	$51.90	$51.90
Purchase #7	$153.32	5.675%	$162.0209	$162.02	$162.00	$162.00
7 purchase totals =	$836.01		$900.6207	$900.62	$900.55	$900.70