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	$240.61	13.314%	$272.6448	$272.64	$272.65	$272.60
Purchase #2	$86.38	5.810%	$91.3987	$91.40	$91.40	$91.40
Purchase #3	$97.37	12.264%	$109.3115	$109.31	$109.30	$109.30
Purchase #4	$48.72	9.279%	$53.2407	$53.24	$53.25	$53.20
Purchase #5	$190.38	3.256%	$196.5788	$196.58	$196.60	$196.60
Purchase #6	$37.52	3.527%	$38.8433	$38.84	$38.85	$38.80
Purchase #7	$5.98	3.365%	$6.1812	$6.18	$6.20	$6.20
7 purchase totals =	$706.96		$768.1990	$768.19	$768.25	$768.10