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	$228.54	4.387%	$238.566	$238.57	$238.55	$238.60
Purchase #2	$90.95	9.279%	$99.3893	$99.39	$99.40	$99.40
Purchase #3	$163.62	4.768%	$171.4214	$171.42	$171.40	$171.40
Purchase #4	$191.71	9.265%	$209.4719	$209.47	$209.45	$209.50
Purchase #5	$190.35	11.551%	$212.3373	$212.34	$212.35	$212.30
Purchase #6	$46.45	12.273%	$52.1508	$52.15	$52.15	$52.20
Purchase #7	$12.40	11.790%	$13.862	$13.86	$13.85	$13.90
7 purchase totals =	$924.02		$997.1987	$997.20	$997.15	$997.30