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	$123.84	6.513%	$131.9057	$131.91	$131.90	$131.90
Purchase #2	$64.51	4.494%	$67.4091	$67.41	$67.40	$67.40
Purchase #3	$232.53	11.569%	$259.4314	$259.43	$259.45	$259.40
Purchase #4	$184.65	13.423%	$209.4356	$209.44	$209.45	$209.40
Purchase #5	$102.49	9.871%	$112.6068	$112.61	$112.60	$112.60
Purchase #6	$34.81	3.388%	$35.9894	$35.99	$36.00	$36.00
Purchase #7	$128.89	3.360%	$133.2207	$133.22	$133.20	$133.20
7 purchase totals =	$871.72		$949.9987	$950.01	$950.00	$949.90