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	$126.77	5.315%	$133.5078	$133.51	$133.50	$133.50
Purchase #2	$241.82	12.708%	$272.5505	$272.55	$272.55	$272.60
Purchase #3	$156.38	12.867%	$176.5014	$176.50	$176.50	$176.50
Purchase #4	$39.72	7.360%	$42.6434	$42.64	$42.65	$42.60
Purchase #5	$152.83	13.119%	$172.8798	$172.88	$172.90	$172.90
Purchase #6	$227.95	6.386%	$242.5069	$242.51	$242.50	$242.50
Purchase #7	$70.44	3.188%	$72.6856	$72.69	$72.70	$72.70
7 purchase totals =	$1,015.91		$1,113.2754	$1,113.28	$1,113.30	$1,113.30