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	$98.81	4.635%	$103.3898	$103.39	$103.40	$103.40
Purchase #2	$40.75	7.209%	$43.6877	$43.69	$43.70	$43.70
Purchase #3	$148.79	4.498%	$155.4826	$155.48	$155.50	$155.50
Purchase #4	$8.42	4.794%	$8.8237	$8.82	$8.80	$8.80
Purchase #5	$173.95	9.720%	$190.8579	$190.86	$190.85	$190.90
Purchase #6	$221.85	7.464%	$238.4089	$238.41	$238.40	$238.40
Purchase #7	$36.98	4.613%	$38.6859	$38.69	$38.70	$38.70
7 purchase totals =	$729.55		$779.3365	$779.34	$779.35	$779.40