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	$89.43	12.145%	$100.2913	$100.29	$100.30	$100.30
Purchase #2	$218.80	3.120%	$225.6266	$225.63	$225.65	$225.60
Purchase #3	$132.77	4.485%	$138.7247	$138.72	$138.70	$138.70
Purchase #4	$186.87	5.127%	$196.4508	$196.45	$196.45	$196.50
Purchase #5	$31.63	6.660%	$33.7366	$33.74	$33.75	$33.70
Purchase #6	$47.98	3.226%	$49.5278	$49.53	$49.55	$49.50
Purchase #7	$56.94	4.840%	$59.6959	$59.70	$59.70	$59.70
7 purchase totals =	$764.42		$804.0537	$804.06	$804.10	$804.00