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	$155.88	11.107%	$173.1936	$173.19	$173.20	$173.20
Purchase #2	$166.74	11.856%	$186.5087	$186.51	$186.50	$186.50
Purchase #3	$50.77	13.209%	$57.4762	$57.48	$57.50	$57.50
Purchase #4	$191.56	12.638%	$215.7694	$215.77	$215.75	$215.80
Purchase #5	$174.90	12.404%	$196.5946	$196.59	$196.60	$196.60
Purchase #6	$214.59	13.157%	$242.8236	$242.82	$242.80	$242.80
Purchase #7	$226.33	7.192%	$242.6077	$242.61	$242.60	$242.60
7 purchase totals =	$1,180.77		$1,314.9738	$1,314.97	$1,314.95	$1,315.00