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	$78.41	5.576%	$82.7821	$82.78	$82.80	$82.80
Purchase #2	$117.60	13.268%	$133.2032	$133.20	$133.20	$133.20
Purchase #3	$229.51	4.772%	$240.4622	$240.46	$240.45	$240.50
Purchase #4	$250.74	5.847%	$265.4008	$265.40	$265.40	$265.40
Purchase #5	$92.97	5.803%	$98.365	$98.37	$98.35	$98.40
Purchase #6	$212.86	12.236%	$238.9055	$238.91	$238.90	$238.90
Purchase #7	$217.40	4.570%	$227.3352	$227.34	$227.35	$227.30
7 purchase totals =	$1,199.49		$1,286.4540	$1,286.46	$1,286.45	$1,286.50