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	$128.38	9.305%	$140.3258	$140.33	$140.35	$140.30
Purchase #2	$237.38	11.419%	$264.4864	$264.49	$264.50	$264.50
Purchase #3	$45.32	9.647%	$49.692	$49.69	$49.70	$49.70
Purchase #4	$210.86	3.159%	$217.5211	$217.52	$217.50	$217.50
Purchase #5	$30.97	4.803%	$32.4575	$32.46	$32.45	$32.50
Purchase #6	$180.88	13.435%	$205.1812	$205.18	$205.20	$205.20
Purchase #7	$71.90	9.789%	$78.9383	$78.94	$78.95	$78.90
7 purchase totals =	$905.69		$988.6023	$988.61	$988.65	$988.60