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	$248.76	3.440%	$257.3173	$257.32	$257.30	$257.30
Purchase #2	$99.43	11.495%	$110.8595	$110.86	$110.85	$110.90
Purchase #3	$84.43	6.377%	$89.8141	$89.81	$89.80	$89.80
Purchase #4	$33.73	9.386%	$36.8959	$36.90	$36.90	$36.90
Purchase #5	$103.53	12.563%	$116.5365	$116.54	$116.55	$116.50
Purchase #6	$235.38	8.472%	$255.3214	$255.32	$255.30	$255.30
Purchase #7	$145.28	11.447%	$161.9102	$161.91	$161.90	$161.90
7 purchase totals =	$950.54		$1,028.6549	$1,028.66	$1,028.60	$1,028.60