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	$182.79	12.115%	$204.935	$204.94	$204.95	$204.90
Purchase #2	$72.31	6.697%	$77.1526	$77.15	$77.15	$77.20
Purchase #3	$35.50	6.139%	$37.6793	$37.68	$37.70	$37.70
Purchase #4	$18.33	12.627%	$20.6445	$20.64	$20.65	$20.60
Purchase #5	$126.53	6.389%	$134.614	$134.61	$134.60	$134.60
Purchase #6	$115.98	6.766%	$123.8272	$123.83	$123.85	$123.80
Purchase #7	$233.64	3.347%	$241.4599	$241.46	$241.45	$241.50
7 purchase totals =	$785.08		$840.3125	$840.31	$840.35	$840.30