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	$78.94	12.189%	$88.562	$88.56	$88.55	$88.60
Purchase #2	$193.29	11.709%	$215.9223	$215.92	$215.90	$215.90
Purchase #3	$142.85	4.114%	$148.7268	$148.73	$148.75	$148.70
Purchase #4	$12.48	10.281%	$13.7631	$13.76	$13.75	$13.80
Purchase #5	$103.65	12.593%	$116.7026	$116.70	$116.70	$116.70
Purchase #6	$26.97	3.206%	$27.8347	$27.83	$27.85	$27.80
Purchase #7	$59.35	13.624%	$67.4358	$67.44	$67.45	$67.40
7 purchase totals =	$617.53		$678.9473	$678.94	$678.95	$678.90