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	$79.93	12.224%	$89.7006	$89.70	$89.70	$89.70
Purchase #2	$51.27	8.590%	$55.6741	$55.67	$55.65	$55.70
Purchase #3	$42.68	6.810%	$45.5865	$45.59	$45.60	$45.60
Purchase #4	$207.83	8.436%	$225.3625	$225.36	$225.35	$225.40
Purchase #5	$40.87	5.646%	$43.1775	$43.18	$43.20	$43.20
Purchase #6	$62.98	13.568%	$71.5251	$71.53	$71.55	$71.50
Purchase #7	$106.90	11.192%	$118.8642	$118.86	$118.85	$118.90
7 purchase totals =	$592.46		$649.8905	$649.89	$649.90	$650.00