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	$236.73	11.416%	$263.7551	$263.76	$263.75	$263.80
Purchase #2	$39.72	5.291%	$41.8216	$41.82	$41.80	$41.80
Purchase #3	$50.90	12.449%	$57.2365	$57.24	$57.25	$57.20
Purchase #4	$38.57	6.395%	$41.0366	$41.04	$41.05	$41.00
Purchase #5	$218.53	10.308%	$241.0561	$241.06	$241.05	$241.10
Purchase #6	$119.78	6.727%	$127.8376	$127.84	$127.85	$127.80
Purchase #7	$85.82	4.628%	$89.7917	$89.79	$89.80	$89.80
7 purchase totals =	$790.05		$862.5352	$862.55	$862.55	$862.50