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	$221.52	12.258%	$248.6739	$248.67	$248.65	$248.70
Purchase #2	$231.98	11.483%	$258.6183	$258.62	$258.60	$258.60
Purchase #3	$150.52	13.111%	$170.2547	$170.25	$170.25	$170.30
Purchase #4	$232.45	4.509%	$242.9312	$242.93	$242.95	$242.90
Purchase #5	$113.64	13.445%	$128.9189	$128.92	$128.90	$128.90
Purchase #6	$38.57	11.183%	$42.8833	$42.88	$42.90	$42.90
Purchase #7	$193.88	13.131%	$219.3384	$219.34	$219.35	$219.30
7 purchase totals =	$1,182.56		$1,311.6187	$1,311.61	$1,311.60	$1,311.60