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	$115.43	5.119%	$121.3389	$121.34	$121.35	$121.30
Purchase #2	$86.55	6.134%	$91.859	$91.86	$91.85	$91.90
Purchase #3	$27.60	13.380%	$31.2929	$31.29	$31.30	$31.30
Purchase #4	$168.49	7.767%	$181.5766	$181.58	$181.60	$181.60
Purchase #5	$193.92	7.522%	$208.5067	$208.51	$208.50	$208.50
Purchase #6	$96.83	13.413%	$109.8178	$109.82	$109.80	$109.80
Purchase #7	$72.75	8.395%	$78.8574	$78.86	$78.85	$78.90
7 purchase totals =	$761.57		$823.2493	$823.26	$823.25	$823.30