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	$94.66	4.160%	$98.5979	$98.60	$98.60	$98.60
Purchase #2	$16.95	9.228%	$18.5141	$18.51	$18.50	$18.50
Purchase #3	$234.97	3.593%	$243.4125	$243.41	$243.40	$243.40
Purchase #4	$53.27	11.573%	$59.4349	$59.43	$59.45	$59.40
Purchase #5	$121.80	12.308%	$136.7911	$136.79	$136.80	$136.80
Purchase #6	$245.55	6.420%	$261.3143	$261.31	$261.30	$261.30
Purchase #7	$46.51	13.475%	$52.7772	$52.78	$52.80	$52.80
7 purchase totals =	$813.71		$870.8420	$870.83	$870.85	$870.80