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	$91.51	10.265%	$100.9035	$100.90	$100.90	$100.90
Purchase #2	$19.31	12.755%	$21.773	$21.77	$21.75	$21.80
Purchase #3	$13.42	11.535%	$14.968	$14.97	$14.95	$15.00
Purchase #4	$173.67	6.858%	$185.5803	$185.58	$185.60	$185.60
Purchase #5	$23.38	11.576%	$26.0865	$26.09	$26.10	$26.10
Purchase #6	$223.54	6.556%	$238.1953	$238.20	$238.20	$238.20
Purchase #7	$109.84	12.372%	$123.4294	$123.43	$123.45	$123.40
7 purchase totals =	$654.67		$710.9360	$710.94	$710.95	$711.00