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	$38.49	9.360%	$42.0927	$42.09	$42.10	$42.10
Purchase #2	$241.43	11.470%	$269.122	$269.12	$269.10	$269.10
Purchase #3	$137.53	10.261%	$151.642	$151.64	$151.65	$151.60
Purchase #4	$76.81	9.167%	$83.8512	$83.85	$83.85	$83.90
Purchase #5	$34.26	5.671%	$36.2029	$36.20	$36.20	$36.20
Purchase #6	$218.71	10.233%	$241.0906	$241.09	$241.10	$241.10
Purchase #7	$216.77	5.592%	$228.8918	$228.89	$228.90	$228.90
7 purchase totals =	$964.00		$1,052.8932	$1,052.88	$1,052.90	$1,052.90