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	$26.56	9.323%	$29.0362	$29.04	$29.05	$29.00
Purchase #2	$52.59	3.686%	$54.5285	$54.53	$54.55	$54.50
Purchase #3	$239.85	10.658%	$265.4132	$265.41	$265.40	$265.40
Purchase #4	$54.45	3.455%	$56.3312	$56.33	$56.35	$56.30
Purchase #5	$209.29	13.723%	$238.0109	$238.01	$238.00	$238.00
Purchase #6	$224.50	7.399%	$241.1108	$241.11	$241.10	$241.10
Purchase #7	$166.58	6.488%	$177.3877	$177.39	$177.40	$177.40
7 purchase totals =	$973.82		$1,061.8185	$1,061.82	$1,061.85	$1,061.70