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	$205.85	9.111%	$224.605	$224.61	$224.60	$224.60
Purchase #2	$187.91	7.427%	$201.8661	$201.87	$201.85	$201.90
Purchase #3	$112.62	13.326%	$127.6277	$127.63	$127.65	$127.60
Purchase #4	$75.89	9.169%	$82.8484	$82.85	$82.85	$82.80
Purchase #5	$199.72	12.192%	$224.0699	$224.07	$224.05	$224.10
Purchase #6	$169.69	9.255%	$185.3948	$185.39	$185.40	$185.40
Purchase #7	$123.93	13.350%	$140.4747	$140.47	$140.45	$140.50
7 purchase totals =	$1,075.61		$1,186.8866	$1,186.89	$1,186.85	$1,186.90