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	$155.48	13.559%	$176.5615	$176.56	$176.55	$176.60
Purchase #2	$34.74	10.357%	$38.338	$38.34	$38.35	$38.30
Purchase #3	$71.51	4.743%	$74.9017	$74.90	$74.90	$74.90
Purchase #4	$73.31	11.625%	$81.8323	$81.83	$81.85	$81.80
Purchase #5	$131.74	7.452%	$141.5573	$141.56	$141.55	$141.60
Purchase #6	$12.90	7.156%	$13.8231	$13.82	$13.80	$13.80
Purchase #7	$79.35	12.618%	$89.3624	$89.36	$89.35	$89.40
7 purchase totals =	$559.03		$616.3763	$616.37	$616.35	$616.40