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	$228.91	4.375%	$238.9248	$238.92	$238.90	$238.90
Purchase #2	$202.84	12.322%	$227.8339	$227.83	$227.85	$227.80
Purchase #3	$223.25	7.769%	$240.5943	$240.59	$240.60	$240.60
Purchase #4	$28.35	9.695%	$31.0985	$31.10	$31.10	$31.10
Purchase #5	$213.72	13.120%	$241.7601	$241.76	$241.75	$241.80
Purchase #6	$192.49	4.360%	$200.8826	$200.88	$200.90	$200.90
Purchase #7	$120.85	10.688%	$133.7664	$133.77	$133.75	$133.80
7 purchase totals =	$1,210.41		$1,314.8606	$1,314.85	$1,314.85	$1,314.90