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	$94.72	5.613%	$100.0366	$100.04	$100.05	$100.00
Purchase #2	$208.43	7.251%	$223.5433	$223.54	$223.55	$223.50
Purchase #3	$176.56	3.319%	$182.42	$182.42	$182.40	$182.40
Purchase #4	$187.53	12.223%	$210.4518	$210.45	$210.45	$210.50
Purchase #5	$241.34	8.591%	$262.0735	$262.07	$262.05	$262.10
Purchase #6	$180.45	3.386%	$186.56	$186.56	$186.55	$186.60
Purchase #7	$250.43	9.712%	$274.7518	$274.75	$274.75	$274.80
7 purchase totals =	$1,339.46		$1,439.8370	$1,439.83	$1,439.80	$1,439.90