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	$18.79	8.567%	$20.3997	$20.40	$20.40	$20.40
Purchase #2	$9.51	4.603%	$9.9477	$9.95	$9.95	$9.90
Purchase #3	$126.82	3.775%	$131.6075	$131.61	$131.60	$131.60
Purchase #4	$60.84	6.147%	$64.5798	$64.58	$64.60	$64.60
Purchase #5	$102.48	6.661%	$109.3062	$109.31	$109.30	$109.30
Purchase #6	$131.69	9.698%	$144.4613	$144.46	$144.45	$144.50
Purchase #7	$7.36	12.790%	$8.3013	$8.30	$8.30	$8.30
7 purchase totals =	$457.49		$488.6035	$488.61	$488.60	$488.60