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	$176.89	6.732%	$188.7982	$188.80	$188.80	$188.80
Purchase #2	$198.39	7.789%	$213.8426	$213.84	$213.85	$213.80
Purchase #3	$90.61	8.266%	$98.0998	$98.10	$98.10	$98.10
Purchase #4	$80.43	8.500%	$87.2666	$87.27	$87.25	$87.30
Purchase #5	$144.35	10.178%	$159.0419	$159.04	$159.05	$159.00
Purchase #6	$128.68	12.632%	$144.9349	$144.93	$144.95	$144.90
Purchase #7	$238.89	8.168%	$258.4025	$258.40	$258.40	$258.40
7 purchase totals =	$1,058.24		$1,150.3865	$1,150.38	$1,150.40	$1,150.30