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	$103.38	13.499%	$117.3353	$117.34	$117.35	$117.30
Purchase #2	$106.26	12.483%	$119.5244	$119.52	$119.50	$119.50
Purchase #3	$152.46	12.691%	$171.8087	$171.81	$171.80	$171.80
Purchase #4	$53.52	10.874%	$59.3398	$59.34	$59.35	$59.30
Purchase #5	$92.66	6.770%	$98.9331	$98.93	$98.95	$98.90
Purchase #6	$209.66	13.318%	$237.5825	$237.58	$237.60	$237.60
Purchase #7	$195.63	9.713%	$214.6315	$214.63	$214.65	$214.60
7 purchase totals =	$913.57		$1,019.1553	$1,019.15	$1,019.20	$1,019.00