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	$176.25	4.336%	$183.8922	$183.89	$183.90	$183.90
Purchase #2	$244.43	10.849%	$270.9482	$270.95	$270.95	$270.90
Purchase #3	$103.99	6.628%	$110.8825	$110.88	$110.90	$110.90
Purchase #4	$28.62	11.447%	$31.8961	$31.90	$31.90	$31.90
Purchase #5	$10.25	7.776%	$11.047	$11.05	$11.05	$11.00
Purchase #6	$63.46	3.388%	$65.61	$65.61	$65.60	$65.60
Purchase #7	$57.32	4.170%	$59.7102	$59.71	$59.70	$59.70
7 purchase totals =	$684.32		$733.9862	$733.99	$734.00	$733.90