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	$121.61	13.168%	$137.6236	$137.62	$137.60	$137.60
Purchase #2	$29.30	12.356%	$32.9203	$32.92	$32.90	$32.90
Purchase #3	$145.46	12.752%	$164.0091	$164.01	$164.00	$164.00
Purchase #4	$85.40	4.753%	$89.4591	$89.46	$89.45	$89.50
Purchase #5	$227.99	5.358%	$240.2057	$240.21	$240.20	$240.20
Purchase #6	$205.64	4.761%	$215.4305	$215.43	$215.45	$215.40
Purchase #7	$249.44	6.409%	$265.4266	$265.43	$265.45	$265.40
7 purchase totals =	$1,064.84		$1,145.0749	$1,145.08	$1,145.05	$1,145.00