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	$51.97	11.368%	$57.8779	$57.88	$57.90	$57.90
Purchase #2	$140.62	3.545%	$145.605	$145.61	$145.60	$145.60
Purchase #3	$247.87	12.373%	$278.539	$278.54	$278.55	$278.50
Purchase #4	$93.30	9.776%	$102.421	$102.42	$102.40	$102.40
Purchase #5	$174.84	5.782%	$184.9492	$184.95	$184.95	$184.90
Purchase #6	$90.48	10.362%	$99.8555	$99.86	$99.85	$99.90
Purchase #7	$128.59	13.859%	$146.4113	$146.41	$146.40	$146.40
7 purchase totals =	$927.67		$1,015.6589	$1,015.67	$1,015.65	$1,015.60