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	$137.30	6.414%	$146.1064	$146.11	$146.10	$146.10
Purchase #2	$46.32	12.726%	$52.2147	$52.21	$52.20	$52.20
Purchase #3	$102.31	3.721%	$106.117	$106.12	$106.10	$106.10
Purchase #4	$87.51	11.803%	$97.8388	$97.84	$97.85	$97.80
Purchase #5	$220.55	9.218%	$240.8803	$240.88	$240.90	$240.90
Purchase #6	$109.28	6.573%	$116.463	$116.46	$116.45	$116.50
Purchase #7	$143.71	10.556%	$158.88	$158.88	$158.90	$158.90
7 purchase totals =	$846.98		$918.5002	$918.50	$918.50	$918.50