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	$35.25	9.608%	$38.6368	$38.64	$38.65	$38.60
Purchase #2	$57.48	3.789%	$59.6579	$59.66	$59.65	$59.70
Purchase #3	$81.79	5.210%	$86.0513	$86.05	$86.05	$86.10
Purchase #4	$72.98	13.251%	$82.6506	$82.65	$82.65	$82.70
Purchase #5	$39.87	7.859%	$43.0034	$43.00	$43.00	$43.00
Purchase #6	$207.91	10.525%	$229.7925	$229.79	$229.80	$229.80
Purchase #7	$249.64	9.797%	$274.0972	$274.10	$274.10	$274.10
7 purchase totals =	$744.92		$813.8897	$813.89	$813.90	$814.00