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	$63.70	13.688%	$72.4193	$72.42	$72.40	$72.40
Purchase #2	$245.62	3.823%	$255.0101	$255.01	$255.00	$255.00
Purchase #3	$109.39	5.639%	$115.5585	$115.56	$115.55	$115.60
Purchase #4	$31.64	4.207%	$32.9711	$32.97	$32.95	$33.00
Purchase #5	$223.65	7.449%	$240.3097	$240.31	$240.30	$240.30
Purchase #6	$103.86	6.361%	$110.4665	$110.47	$110.45	$110.50
Purchase #7	$117.34	12.450%	$131.9488	$131.95	$131.95	$131.90
7 purchase totals =	$895.20		$958.6840	$958.69	$958.60	$958.70