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	$29.81	8.417%	$32.3191	$32.32	$32.30	$32.30
Purchase #2	$183.39	3.763%	$190.291	$190.29	$190.30	$190.30
Purchase #3	$228.96	9.838%	$251.4851	$251.49	$251.50	$251.50
Purchase #4	$137.37	9.506%	$150.4284	$150.43	$150.45	$150.40
Purchase #5	$188.72	11.743%	$210.8814	$210.88	$210.90	$210.90
Purchase #6	$198.39	12.502%	$223.1927	$223.19	$223.20	$223.20
Purchase #7	$138.92	8.122%	$150.2031	$150.20	$150.20	$150.20
7 purchase totals =	$1,105.56		$1,208.8008	$1,208.80	$1,208.85	$1,208.80